prot warriors don't have very high DPS so this isn't that great an idea. Sure, you may take forever to die, but if you can't kill the boss, whats the point? When you aren't tanking you aren't taking direct physical melee damage so all the avoidance & mitigation doesn't do much. You will also have rage issues on bosses who don't AOE much.

Most heroic end bosses have gimmicks like dropping aggro, healing themselves, massive AoE magic damage, casting diseases/curses/poisons, etc that make me think a team that has no "heal someone else" ability will have a crazy hard time. In heroic mode, frenzied regeneration just isn't enough to keep tanks up from boss hits -- for example Trollgore hits 5/5 T7.5 geared prot tanks for 10k a swing, every few seconds. You'll survive maybe 20 seconds w/ shield wall etc before you die. Remember as well shield wall getting nerfed in 3.1.