My big issue with it is offensive players pushing another offensive player. I've never been OK with it, even when our offensive linemen were stacking into a beast mode pile to get marshawn some more yards.
Teams that try to come up with something to stop it, like trying to time the snap, get penalized to the point of threatening to give the Eagles a free touchdown. (Redskins/Eagles playoff game)
I've said it before - I am NOT condoning this, but I'm waiting for some defensive coordinator to convince a couple of his guys to ignore the play and go for the QBs head. The first time a QB is left on the ground after the rest of the pile moves away, this play stops.