These are people ostracized from less extreme groups. The only places they find acceptance is with people like them, leading to an echo chamber where the most insane ideas can fester and grow. I think the solution to the issue of having extremists among us is to do the hardest imaginable thing and accept them into our communities and keep it positive and short when correcting things. "I hope that kind of thing doesn't hurt a lot of people." Or whatever. We're silly animals who will do anything to be accepted by our chosen group including learning to think differently.