I’ve seen a forum where the Admin pinned a banner (to appear on every page) that no one could unpin. It was posted for 30 days explaining the negativity and reminding everyone of the Terms & Conditions of the forum… and that should anyone continue with the negative and disparaging comments about others, that user will be suspended. Suspension can be for a week, 2 weeks or a months (Admin’s discretion). Future violations of the T&C and the user will be permanently banned. It seemed to work out just fine. The atmosphere and discourse got back on track without the user having to be suspended or banned.
I think by keeping that banner pinned for 30 days also served as a reminder to everyone else. Even after the banner was unpinned, there were no more problems. Maybe they were lucky?
Conspiracy theorists are probably the hardest to handle as they are firm in their believe of the conspiracies, whether it relates to politics, health or other topics.