It's not helpful to palm this off on mental illness - that does a disservice to people with such issues and doesn't address the fact that virulent ideologies exist in the real world and have proponents that are capable of planning, organizing, and recruiting.

Sure, 8ch is also full of autists who just need a hug (subject to certain terms and conditions) but if I discover that a bunch of people are making plans to kill me I'm not under any obligation to put my enemy's problems ahead of my own survival.