I. Introduction
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It has been argued that, in theory, interactive fiction should be able to do anything that static fiction can do, as static fiction amounts to interactive fiction that consists of one move (>READ STORY) and more interaction should enrich the storytelling experience, not limit it.  The merits of that proposition can be debated, but there's certainly substantial truth in it, and it follows that most of the techniques and subjects that can be usefully employed or explored in the realm of static fiction should be adaptable to interactive fiction.
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One area of static fiction for which there are, thus far, few or no analogues in IF is argument or propaganda (the latter generally construed as a pushier and less nuanced form of the former but not a different animal as such).  Examples of the form in static fiction include Orwell's 1984, Solzhenitsyn's Cancer Ward, or Rand's Atlas Shrugged.  Most static fiction that makes an argument doesn't function solely in that capacity, of course, but in each of the above examples a position of some complexity is staked out.  Can IF do the same?  Theoretically, there's no inherent reason why not, but the potential IF propagandist should be aware of potential limitations on the form, many of which apply to static fiction as well.  Fiction as argument lends itself better to certain types of arguments than to others, and recognizing what kinds of arguments are best made through fiction, whether static or interactive, will likely make both for a more effective argument and for better IF. At the same time, however, the nature of IF allows for storytelling that in some ways is well suited to argument, as the player is capable of directing the story in multiple directions, and the author accordingly has the power to characterize those directions as more or less positive, depending on how they fit into the argument.  The trick, of course, is to not only communicate what the author thinks, but to communicate it in a way that tends to persuade.
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In the first section, I discuss common types of argument, and the structure of each such type.  The second section discuss specific examples of IF that has attempted certain forms of argument, and the third section examines some considerations and potential pitfalls in attempting to persuade through IF.
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II. Categories
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Argument in fiction may be generally stated as that which attempts to persuade the reader of the truth (or falsity) of some proposition external to the work itself; that Dickens convinces me in Tale of Two Cities that Sydney Carton is at bottom a good man does not make that novel an argument for that principle.  The French Revolution, however, does (did) exist outside the novel, and to the extent that Dickens attempts to convince the reader of something about the French Revolution, the book functions as an argument.  In that case, the argument, depending on one's view of the novel, might be that the Revolution began as a middle-class uprising and was coopted by radicals, or it might be that political revolutions tend to victimize those who have supported them most loyally, or it might be something else entirely.
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One common type of argument is policy-based: this or that program or policy should be adopted or eliminated because it will achieve the greatest good for the greatest number.  In fiction, this might be done by simply dramatizing the effects of the policy or system in question, whether good or bad, and dystopias-1984 among them-are one of the best-known forms (though some dystopias are better than others about explaining what it was that set off the downward spiral and how the causal chain worked).  Dystopia has been attempted in IF, but not often; Infocom's A Mind Forever Voyaging is probably the best-known example.  A similar type of argument in a different time frame is the historical argument: effect A was the result of cause B, not cause C, which led to effect D but not to E or F.  Again, fiction tends to do this by dramatizing the causes and effects in question: Tale of Two Cities is arguably a case in point, as are the Shaara novels depicting the American Civil War.  IF, to my knowledge, has not attempted an argument of this nature, though some aspects of Jigsaw-in which the player labors to prevent history from being altered-come close, in that they implicitly posit that history as we now know it depended on a certain event. (In that most of the events are obvious historical turning points, it's not a particularly daring argument, and even when they're not the game doesn't really spell out an argument about why those events changed the course of history.)
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Philosophical arguments, by contrast, tend to depend less on factual results and more on the inherent merits of a principle or idea: generally, the point in a philosophical argument is that some principle is sufficiently important that it trumps other admittedly important principles.  To some extent, Daniel Ravipinto's Tapestry was an argument of this type: the game gave you three options that could plausibly be connected to emphasis on different principles, let you choose one of them, and dramatized why the author thought that two of the choices were suboptimal.  Stephen Granade's Losing Your Grip similarly made a pitch for a certain principle, albeit in a rather indirect way.  Religious arguments can take either form: they can argue for a factual proposition that underlies a certain religious belief (the existence of God, say, or the truth of a certain historical narrative central to a given religion), or they can argue for a value proposition (that the existence of evil is consistent or inconsistent with the notion of a just God).
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What is the importance of this distinction? Simply that fiction is generally better suited for arguments that advocate general value propositions than arguments from factual evidence, as fiction, almost by definition, is directed toward single instances rather than comprehensive treatments.  If your policy argument is that a welfare system is good because it helps more people than it harms, it's simply too easy to paint a portrait of people being helped by such a system, and the reader is liable to think that the game hasn't proved a thing.  If your historical argument is that the Treaty of Versailles led directly to World War II, it's too easy to paint fictional scenes illustrating the progression (angry destitute German workers voting for the Nazis, etc.).  An argument that a welfare system is good because a society's profoundest moral obligation is to its poor, however, could well be done through fiction in general and through IF in particular; portraying the importance of such a system in a particular instance can illustrate society's obligation, and the author need not demonstrate that the scene portrayed is perfectly typical.
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III. Examples
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Certain types of arguments are often made primarily through one mode or the other, but not invariably so, and Tapestry is a prime example. There, the game gives you the chance to relive certain key moments in your life, and poses the question: is it better to (1) undo your choices, (2) make the same choices and accept culpability for the harm done, or (3) make the same choices and (essentially) reject the urge to feel guilty.  As mentioned, there are philosophies, or at least ideas, that can be roughly equated with each of those approaches: the first is vaguely humanist, the second is stoic, the third could be described as a notion of self-actualization (one that appears to value highly the making of choices and sticking by them). (Tapestry confuses things considerably by associating the first path with Lucifer and the second two with the Fates of Greek mythology-somewhat sensibly in the case of the second path, not so sensibly for the first and third.)
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The game favors the third option rather emphatically, but it does so by piling bad consequences on the first two options, which amounts to stacking the deck. If the player takes the first path, he or she doesn't actually do much good for anyone by changing the choices at issue, it turns out; lots of bad stuff happens anyway, it just happens to be slightly different bad stuff. The author is free to make that argument in the context of the game, but it has nothing to do with a value proposition that goes beyond the game; to the extent that the game can be taken as an assertion that any such attempts to undo the consequences of one's actions are ultimately futile (even in a non-supernatural context), it's a highly questionable assertion.  It would, in other words, be easy enough to set up a factual scenario where revising your choices led to unambiguously better results; with hindsight, in fact, that would appear to be the more natural conclusion.
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The favoring of the third over the second path is slightly less fact-dependent, as the game makes the case that the way the protagonist handles his choices is more important than the choices themselves-but the deck is still stacked to some extent, as the choices amount to handling those choices either really poorly or reasonably well.  That is, there's an argument to be made against simply rejecting guilt outright, which seems to be the course the author favors; the protagonist might instead decide to accept guilt and view it as a necessary consequence of making mistakes, a reminder that helps him avoid the mistakes in future.  Guilt might drive him to be a better person, make better decisions.  Here, though, the alternative to rejecting guilt is being completely racked with guilt to the point where self-hatred consumes your life, which doesn't make for a particularly nuanced argument.
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All of this doesn't make Tapestry a bad game as such-it functions reasonably well as an exploration of moral decisionmaking.  Forcing the player to make the PC's choices is sometimes genuinely wrenching.  But it does not work as an argument, even on the game's own contrived terms: it's hard to imagine anyone being convinced by Tapestry that, even if one had the chance to change things, it's better to leave key life decisions the way they were, let alone (if this is a fair real-life analogue) refusing to undo a decision that appears to have turned out badly.  The major premise of that argument, that things will turn out badly anyway, is simply an assumption-unfalsifiable, under the circumstances, but pretty strongly counterintuitive.  The game's other argument, about guilt, is no more persuasive: while it turns on a value proposition rather than on a factual assumption, it oversimplifies that proposition to the point of meaninglessness.
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Equally ineffective, though for different reasons, is the argument in A Mind Forever Voyaging, where the protagonist is a computer asked to explore the future.  A prominent politician has proposed a Plan to cure the nation's social ills, and a researcher has managed to simulate the future as it would be under the Plan and commissioned you to go explore the simulation.  It turns out, of course, that everything goes to hell under the Plan, and so I suppose you could say that the game serves as an argument against the substance of the Plan (which amounts to a somewhat more draconian version of law-and-order proposals popular with conservative American politicians), though I hasten to add that this argument probably wasn't primary among the game's intentions.  To the extent that it does so serve, though, it's a thoroughly ineffective argument, as the game makes no attempt to convince the player that the simulation is accurate; insofar as the player is later asked to act on what he or she has experienced, the game more or less asks the player to take it on faith that the simulation is being fair.  (I half-expected a twist at some point whereby it would be revealed that Plan opponents had stacked the deck.)  Moreover, obviously, it's impossible to argue cause-and-effect on this scale; there's no good way of making the case that the law-and-order plan led to the social implosion that the game describes.  The argument therefore hinges primarily on the game hurling certain facts at the player-the simulation is accurate, the policies in question are the primary cause of a certain result-which raises the question, for a skeptical player, about whether those facts tell the whole story.  (In a science fiction story, naturally, they don't.)
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Could the argument about law-and-order policies have been made more effectively as IF? Not in ways that resemble AMFV, probably, but there are other ways.  A depiction of a newly built prison, for instance, where first-time offenders are indoctrinated into a criminal culture during their unjustly long sentences-or a portrayal of the deterioration of the first-time offender's family during that same prison term.  An account of the trial of one such offender, as represented by an incompetent and overworked public defender.  A story in which the offender is along for a ride with his bad-influence buddies and ends up taking the rap along with them.  Most of these stories take a representative case rather than attempting to make a case about all of society, as in A Mind Forever Voyaging, and in these examples the facts are sufficiently commonplace-I doubt anyone would argue that those things don't happen with some regularity-that no one would argue that the plot was concocted solely to serve the argument.  The point is to make an argument about generally accepted or commonplace facts without having to prove exactly how common they are; if your argument turns on the (unprovable) notion that a certain percentage of imprisoned first-time offenders emerge from prison as hardened criminals, it's unlikely to work as IF.  If, however, it arises more from the value judgment that rehabilitative efforts are a better investment of society's resources than more prisons (as illustrated by, say, a parallel story about an offender in a less punitive state), then it might have a shot.
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Could this work for religious arguments as well? Religion is something of a special case, as the scope of the argument tends to be immense; if the game sets out to argue that a certain religion's view of the world is true (and, by implication, that the views of other religions, to the extent they are inconsistent, are false), and it attempts to make its case by portraying the world, it has an awful lot of ground to cover.  Charges of deck-stacking in these cases are virtually inevitable, and Jarod's Journey, a piece of Christian IF entered into the 2000 competition (which announced its intentions up front, stating that the game "will hopefully get you and Jarod closer to God") was criticized for precisely those reasons (and many others as well).  To be fair, Jarod's Journey's take on Christianity was so simplistic that it barely qualified as an argument: the player was given a few options to take, and was periodically told whether the author approved of the player's choices.  To the extent that the result was supposed to persuade the player of the merits of Christianity (by modeling a Christian's decisionmaking), while it was spectacularly ineffective, it did attempt to make a case for a proposition; the problem was that the proposition (the truth of Christianity) was too vast to argue coherently.
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How could it have been done?  Perhaps, rather than presenting the entire worldview as a fait accompli, by taking certain aspects of the Christian understanding of the world (or those of another religion) and embedding them in a fictional setting, as the Chronicles of Narnia did.  I.e, the major figures and events in the religion's central story might have analogues in the fictional world, and the player could be encouraged to view those characters and events in the same way as adherents of the real-life religion do. (I'm told that one of the few works of IF to deal with religious themes, The Legend Lives!, did something similar, though I have not played that game.)  The result is likely to be a fairly watered-down argument, however; a reader can perfectly be well enjoy or be moved by Narnia (or, I suspect, The Legend Lives!) without becoming any more convinced that certain religious beliefs are true, or even (in theory) realizing that the author had any particular beliefs.  Transposing religious beliefs into fiction does avoid the problem of requiring the player to accept propositions external to the game, though, and as such it may be the safest approach.
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A more fruitful approach to religious argument in IF might be to confine the argument to propositions internal to the faith, in which case, of course, the external propositions could be assumed to be true.  Such a game might, for instance, question the extent to which a certain practice really comports with doctrine by forcing the player to justify his or her actions to a skeptical NPC.  Alternatively, the game, by portraying a God who decrees certain practices or wills a certain state of affairs as inconsistent with how God is generally pictured within that faith (damning unbaptized infants, say, and coming across as less than loving), might make the point that the practice or state of affairs is in tension with the larger picture.  In either case, the focus is on a value proposition and its consistency with a larger system of beliefs, not on proving facts.
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IV. Other Considerations
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I have suggested that an author seeking to persuade through IF should attempt to make his case by pushing certain value propositions rather than making a factual case. The problems with the latter are, I think clear, but the question remains: would the former approach lead to effective arguments? Maybe, maybe not; a lot of what I have outlined above seems at first glance like the stuff of sentimental TV movies or wartime propaganda films, and no little skill on an author's part is needed to avoid that feel.  The difficulty, to a great extent, in making an argument that turns on a value proposition is that, to make it stick with a general audience, the author tends to want to sell the value in question too strongly.  Ergo, the kid who gets thrown in jail because of an incompetent public defender wouldn't just be a kid, he'd be an honor student who's captain of the baseball team and tutors younger kids-but you see what I mean.  The other facts are essentially a distraction from the value proposition in question, which is that the poor quality of legal representation for the indigent makes attempts to reduce crime by stiffening sentences unfair and unjust.  The purer form of the argument would be to make the same case for a troublemaker kid who has no obvious future and who isn't particularly sympathetic, to show that people deserve adequate representations even when their stories don't tug at the heartstrings-but the trick there is to actually get the argument to come across without obvious editorializing about the importance of assuring the availability of free legal services.
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I'm confident that this can be done, but, in light of the paucity of IF argument of any sort, I'm hard-pressed to point to actual examples.  One well-done game with an argument of sorts at its core is, as mentioned, Losing Your Grip, where the protagonist (at least, as I see it-the author has avoided endorsing any particular interpretation, but this one seems reasonable to me) is engaged in a lengthy process of cleaning his own mental and emotional house and makes some surprising discoveries (surprising even to himself).  Namely, he discovers that problems that he had long blamed on others are to a large extent his own fault, and that the image he had constructed of his father wasn't entirely fair or true to reality.  (Part of what makes this interesting is that the housecleaning wasn't wholly intentional-it was the result of an experimental drug treatment that was supposed to help the protagonist stop smoking.)  The father does not, however, come across as particularly sympathetic, and the reconciliation (to the extent it happens) is hardly driven by a recognition that he is a misunderstood saint; the protagonist's image of him may have been distorted, but he's still fairly unpleasant.  Nevertheless, the game manages to make a case for the propositions that trying to mend a broken relationship is worth the trouble and turmoil, and that letting go of old wrongs is better than holding on to them.  Not wildly controversial propositions (when divorced from the specifics of the game), but not entirely truisms either.
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How does it do that?  Partly by depicting the alternative as destructive to all parties, but also by explicitly depicting the father separately from the distorted image of him that the protagonist had been carrying around (an image which the game portrays as a character in its own right).  The villain of the piece becomes the image, rather than the actual person, and once the image is vanquished, it's suggested that the protagonist can see things as they are and rationally decide to patch things up.  The decision to reconcile with the protagonist's father does not, however, turn on a sympathetic depiction of him; the only such depiction that the game offers, as far as I can tell, comes after the decision is made, which makes reaching out to him somewhat akin to a leap of faith. (Part of what makes Losing Your Grip clever is that the distance between player and protagonist-since the player can reasonably be seen as an aspect of the protagonist that is brought out by the drug treatment-effectively permits the player to make the argument to the protagonist, by making certain choices within the game about how to view the protagonist's father.)  The game continues whether or not the player achieves those insights, however, and since it isn't obvious that the choice was even offered, it's easy to miss the argument.  But the choices are there, and the different outcomes at the end-violence and pain on the one hand, an extra scene offering additional insight on the other-suggest that the author did not view all of the choices as equally desirable.  And since the argument does not depend fundamentally on the facts underlying the protagonist's relationship with his father, it would be unfair to say that the game loads the dice in its portrayal of a particular situation.
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V. Conclusion 
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Arguments can, of course, take a variety of forms, and the case made in Losing Your Grip is fairly abstruse-enough so the aspiring IF propagandist may not find it a useful model.  In addition, again, the case made there is unlikely to be profoundly controversial.  But that game does show how a skillful author can use the techniques of IF to persuade, for example by letting the player see the world differently from the PC and having the player correct the PC's delusions-and the limited nature of the argument underscores the limitations of any fictional form, including IF, for persuasion. 
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