I'm not sure many of these folks are professional trolls. I think many of them are just arguementative, or so set in their ways that they can't be reasoned with. Usually I can tell after a few posts whether these folks can be persuaded as the Waspman suggests, or are a waste of time.
I do agree with you that there are a few earthfirst and peta trolls around, but they usually don't last long here.