The problems didn't exist as much because people didn't usually come across communities they hated/disagreed with unless they were searching them out, and every community could set the standards it wanted to set. And I think that's where large social media sites can't work; they put a bunch of groups, many of which deeply disagree and dislike each other, on the same site/platform and have to try and keep the peace without said groups getting into flame wars and personal attacks 24/7.

Small, indepedently run communities could set their own standards, and those that who disagreed with any one set of rules could go and find somewhere more to their liking. Reddit and Discord have this to an extent, but even then, it's too centralised and too heavily controlled by one organisation.

Hopefully if Mastodon takes off, federated services will bring this style of community back, except with the ability to take part in other communities if people agree with that.