Don, there's some interesting reading about "trolls" at About Trolls. Here's some highlights:

Trolls are utterly impervious to criticism (constructive or otherwise). You cannot negotiate with them; you cannot cause them to feel shame or compassion; you cannot reason with them.

Another problem is that the negative emotions stirred up by trolls leak over into other discussions. Normally affable people can become bitter after reading an angry interchange between a troll and his victims, and this can poison previously friendly interactions between long-time users.

Finally, trolls create a paranoid environment, such that a casual criticism by a new arrival can elicit a ferocious and inappropriate backlash.

The only way to deal with trolls is to limit your reaction to them and by reminding others not to respond to trolls.

When you try to reason with a troll, he wins. When you insult a troll, he wins. When you scream at a troll, he wins. The only thing that trolls can't handle is being ignored.