Charlie,

This is a private forum that was first set up by the MtGox people (I think, someone correct me if I'm wrong), and it's managed by the admin they appointed.

It is Theymos' right and obligation to remove those who are harming the quality of these forums.  The ban was not a result of bias, there were plenty of neutral reasons to ban Goat: he was trolling and belligerent.  Just because Theymos has a personal disagreement with someone does not give them ban-immunity or a free pass to troll.   He did the right thing.