it is always been, play want you enjoy.  if you dont enjoy the prot spec, i would suggest switching, however if you enjoy beeing the main tank then stay prot.  Even in BG, it is still good to be the turtle with the flag.  I am disc/holy spec, adn enjoy it a lot.  I actually have found my survivability better, and more helpful in bg.  to me, it makes since to have a prot spec warrior, or druid be primary with flag, as you are harder to bring down, especially if you are getting shielded and healed.  When you have 7 ally pounding on you though, it doesn't matter what spec you are, you will probably die.  So bottom line, play what you enjoy, adn keep the game fun for you.  Its all about working together with the gear and specs we have, and having a good time.  if you are not enjoying your build, then you should switch, i know i did.