It's quite easy to make edits which seem legitimate, accurate, and NPOV, but are actually nothing of the sort.
From a purely pragmatic point of view pre-emptive bans just aren't an
effective way of fighting this. Anyone can get a new user-name and/or IP-address. Permanent bans aggravate users and make them more likely to resort to underhanded tactics.
Staying wakeful, checking sources and having wikifaith is really the only thing we can do.
Regards, Haukur