People who are legitimately shitty, people who hurt others callously or who hold appalling views about the world, still deserve community and positive human contact. You do not personally need to be the person who holds community with them, and the people who do should take some responsibility for pushing them to be better. But they do not deserve to be ostracized. Expecting others to ostracize them is both unrealistic and cruel.
This is both a question of human dignity—social contact is a necessity for healthy human functioning as much as shelter is—and a question of tactical effectiveness. Yes, there do exist people who are so far gone no intervention will help. But that's not most people, even most people who are legitimately bad. If we have no mechanism to pull people back when they start doing or thinking shitty things, no way for anyone to say "we care about you and we will help you stop this", then we're just ceding everyone to the reactionary milieu the moment they make the slightest inroad.
(obligatory caveat: yes, this changes once they are fully nazis, which is to say once they are organizing towards eliminationist agendas or whatever. that's not what I'm talking about. I'm talking about abusers and republicans)
