He's still there because he has value. He is the only representative of the Left. Like it or not, idiots like him have controlled the country for most of the last 50 years.
Moreover, I believe we would be in violation of Bob's rules if we talked about the Farters and their posts without giving them an opportunity to respond. (Someone can verify this if they want, but I think I remember it from way back.)
As Zimbler put it, BAF is a "free fire zone" - though zz (or anyone else) would be banned if his only purpose was to disrupt the board. I don't think that's the case.
But he isn't hurting anyone. He's a tempestuous child who doesn't know how to conduct himself in public. His parents apparently never civilized him.