The Fediverse already has these, there are lots of echo chamber instances that automatically block other instances for simply federating with the “wrong” instance (equivalent to those AutoMod bans on Reddit for posting in a certain subreddit). Since instance admins pay for their instances out of pocket, they are more restrictive with their instance’s allowed content than social media websites that want to cast the widest net. Eventually, there will be a massive split between communities, like how conservative and progressive Mastodon instances all block each other. Centrists can just have an account on each side of the wall.