Maybe at the start they will be a bit rough around the edges that i agree with, but the hope is that a smattering will improve or find they are great tanks.
Those we have had over the last week who suck and always find they get kicked or wipe not clearing any content will very shortly move back to their other main role.
so just wait it out a bit. Ive tried tanking on my druid (with appropiate gear that i saved from off spec rolls and some of auction house) i didnt do all that well and i stopped because i saw how much harder i was making things.
Now if a bad tank finds that he can never get even 1 boss down. he wont stay tanking thats for sure.