In my experience, trolls (and, closely related, those who thrive on controversy)
continue to thrive because controversy is always readily
available... or even made-up. From the genuine troll who wants
to smash as many buttons as possible to the people who have to
have it their way all the time, they're unavoidable.
Although passive ignoring is effective from a continuance
standpoint, these types have an effect on the general community
that can't be ignored. They implicitly cause members to become
less trusting, less fault-tolerant, less willing to help their perceived
stooge. The trolls and controversy-thriving folk go away
eventually, but the side effects associated with them don't pass
Me spell chucker work grate. Need grandma chicken.