I think that the player in question was acting in character and that, in principle, there was nothing wrong with what he did.
From an in character perspective, a Judge, to my knowledge, builds the infrastructure needed to do his job. That includes banning people. By the time this infrastructure is in place a variety of minor nobles and officials have rightfully been given orders to follow this guy’s instructions. These officials should not, in my opinion, suddenly stop obeying the judge just because some of the nobles of the realm call him a traitor. If he lays out a ban for half the realm these officials will do their best to see it enforced as long as he is the resident judge. Once some mechanic is used to remove the Judge from office then the these officials will rightfully stop taking orders. That is when the time comes to fix the damage done.
At the same time I like the time restriction Tom put in place. It is logical but does not completely remove all power from the judge. I still do not see the players actions as abuse though. When I play a game amongst friends I am often set back by their actions. I seldom howl about how unfair it was and seek for the non-existent master of games to come and set it all right. No rules were broken and everything was done with an in character motive and it all seems very believable to me.
EDIT: Perhaps I misunderstood… Did he ban EVERYONE from the realm then leave in an attempt to destroy the kingdom? THAT would be abuse of mechanics in my opinion. Banning many of the nobles, especially key nobles, seems perfectly ok to me though…
