Pulling groups is a jerk move, plain and simple. If the tank is too slow, there are other ways to get him to speed up, like: I tell the tank in /p to "just keep pulling man, healing is no problem". The first time you pull in me, i'll rescue you, but the second time, when it's obvious you're doing on purpose, I'm going to let you tank 'em.
And random heroic pugs also means varying levels of skill. As long as the tank is pulling at a consistent pace, a little patience is expected from the rest of the group. Not every tank has the experience to chain pull all the way through an instance, or even judge the best speed that the dps/healers are capable of moving.