And as far as I'm aware, chow chows and German shepherds deserve a worse reputation than pit bulls, rotties, or dobermans, yet they're not generally banned. Figure that one out. I'd imagine someone important (read: politician, news editor, etc.) was victim (direct or indirect) to an attack and started a campaign get a particular breed banned, and it went from there.

(I'd also be tempted to maintain that most dogs can be trained to avoid such viciousness at an early age.)