There's a bit of a flamewar on the +Debian private mailing list at the moment, which I think +Steve Langasek beautifully obliterated:
"The primary purpose of a ban is not to teach; it's to protect the lists, as the valuable commons they are, from behaviour that ruins them for everyone.
If someone learns from being banned, that's a beneficial side effect; but it's only a side effect. Our mailing lists are not Kindergarten, it is not our responsibility to teach people how to play nice with others. That's a life skill that should be a precondition of participation."