Tolerance

On a social/human level, a time-limited ban has been found effective on at least one site. It helps reform behaviour of those who are merely ignorant rather than wilfully misbehaving.

It's certainly worth expending some effort on this: LWN comment quality is one of the major features of the site, and as you start to lose the battle the ones misbehaving increasingly get the feeling their behaviour is tolerated or even appreciated. This is a slippery slope, and only LWN features can fix it.