To those who want to preemptively ban people from social networks based on their beliefs/associations, google Megan Phelps. Engagement with non-bigots etc on Twitter changed her, and removed a warrior from the side of the bad guys. That's so much less pain she'll now ever cause the same people you want to protect. But yes, many people had to endure her crap to open the door to this change. Do more people change by being shunned than conversation? Do bigots win arguments? Are they persuasive?