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 as easily.

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Me spell chucker work grate. Need grandma chicken.