I think its a bit of a context rules kind of situation.

In general a non-tank pulling by accident the Tank should grab them. But if they are frequently doing it, to force a tank or heal to do more then they are comfortable with, then thats griefing.

End of the day, its about balance and no one has the right to force a singlular pacce on the rest of the party. If DPS dont like the pace. Well they can leave the option is up to them.

Obviosuly the reverse is also true. A tank refusing to tank because of a single accidental pull then thats griefing too.

Bottom line is there is no hard written rule about it either way, so you can either communicte and come to a decision or you can be petty about it.

Most duties are only 20-30 minutes anyway so if you dont have time for it when you queue, then thats on you. Either way i wish people would just accept it happens and move on after it does.

You are never going to get the player base to 100% conform to your way of thinking