people need to realize that ret doesnt just bring damage, you bring another devo aura, can self heal yourself if shit hits the fan, bop/sac people who need it, lay on hands, and the list goes on.
name another melee spec that offers as much utility as that to the raid. also, the damage is far from bad, it's actually quite strong with gear. I think that GM just has a bad perception about the class, as far as tanks go, you offer strong self-survivability, and cooldowns. I cant see why you'd be turned down for being a paladin tank.