A ban simply would not work as IP addresses can be masked / changed and another credit card used. As for banning "objectionable" posters - although the QAZTwat surely is, you can't define objectionable as a majority view; Say there is a madly bullish thread and one poster is posting a short case (sensibly and objectively)the he might be votes as "objectionable", clearly not right.
The best solution here is to locate him and have a full and frank exchange of views, in person, and very physically,
By the way, can anyone give a steer on the removed postings? I presume it was an insane ramp?