Then let me rephrase:
Is it still murder if you kill a murderer?
Depends upon the conditions, of course, since the very word "murder" implys an unjust killing.
Indeed. I would consider counter-trolling to be fighting fire with fire. Killing the murderer, while he is in the act of attempting murder. NAP as applied to forum behavior. If you initiate trolling, you should not be surprised, nor complain, if you get trolled back.
I do see your point here, and I actually do agree. However, I must point out that our resident Krugman fan is correct; it's still better to not feed the troll, even if you have the right to respond in kind. Trolls are often only after the joy of causing an emotional response, and ignoring them simply removes the reward for this activity.
Indeed, simply ignoring them is the moral "high road," and will, in the long term, cause them to stop, or at least greatly reduce, this sort of behavior. But counter-trolling works just as well, if not better, and is a
lot more fun.
Tit-for-tat, after all, calls for response-in-kind.