...derived from a comment I received from a fellow traveler on the interblogs who has seen an argument I was engaged in:
If you kick somebody out of your discussion (that was me, incidentally) and tell them not to come back to your blog (I haven't), it's considered to be in poor taste to attack their character in continuing comments.
It's a matter of self-respect. If you can't respect yourself, respect troll control, people. Even -I- am tempted to start trolling this person with false accounts, through proxies if necessary. (I will not; while it would be entertaining to engage somebody so easily tweaked, it would be in poor taste. Rather like the comments to begin with.)