I agree with a lot of your post, however:

• Highlighting past mistakes

Highlighting past mistakes isn't necessarily a bad thing to do. Some of our worst offenders here continually post the same nonsense responses, which the uninitiated (those asking for help) would take at face value, despite them having been educated/proven wrong many, many times. Having spoken to some people at TPCiG last year about this sort of behaviour in communities, including Gloria & Larry Wall (yes Your Mother, I know...), this sort of behaviour is just not tolerated elsewhere, along with many of the other bad behaviours you list. They all went down the road of taking action. Personally I think that failure to exclude repeat offenders is more damaging to the site and the wider perl community than any gains from just letting people continually exhibit bad behaviour. There are other examples where I believe highlighting past mistakes is appropriate, for example along the lines of 'The definition of insanity is doing the same thing over and over again, but expecting different results.'.