I think we should allow heterodox beliefs in public forums since at least this reduces the effect of echo chambers. The other alternative is to ban certain ideas from the mainstream, but I think this leads to groups like Nazis just moving to dedicated sites where their ideas are reinforced.
Like I’d rather see a Nazi subreddit where those ideas are likely to see more challenges, than some random Nazi site where bad ideas metasticize in the shadows. Maybe the spooks prefer it this way since different sites makes it easier to categorise people.