I don't see a problem with it being player driven, to be an effective griefer you need a high lvl char, if you ruin your reputation with griefing, its your problem. If you cant remember names of griefers, your problem too. But stuff like banning players because they picked up a shield while duelling is just over the top (did happen).
(Only obvious stuff like interrupting duells should still be punished, as this part of griefing can not be avoided by the players)