Many of the problems with Internet communities today stem from the fact that they are in places which don’t belong to the members. Youtube and twitter are nothing without their users, but Youtube and twitter are free to reject someone or change their standards of what is acceptable at any time, and users have no grounds to challenge them. Years of work can be deleted or hidden in a moment if the owner sees fit, and standards of behaviour designed to keep billions of people clicking are never going to be the ones which a small group of nerdy people chose for themselves. Moreover, its not in the interest of these companies to let users export their work in a convenient format.
Alexiares suggests that a good first step would be moving to services hosted by the post office or the public library. The public post has its problems, like the times it was used to block the spread of birth control information and equipment, but libraries and the post office at least have a tradition of offering service and privacy to everyone on equal terms, and are at least based in the same country with the same laws as their users- I don’t think that Germans and Americans will ever agree on what is protected free speech, or people in Ontario and people in Fars will agree on who can bare which bits. So decentralizing onto services like mastodon could help.
When I think back, though, it seems to me that this is a much older problem than centralized social media. In the 2000s, communities sprang up in places like the comments sections of blogs or the off-topic section of forums. Often, the owners of those sites are not happy about this at all, because moderation is work and organizing moderators is work and they have plenty of underpaid work of their own to do (the Taylor family shut down comments on their main site for this reason). Other times, they create a monthly thread or a members-only subforum to let their readers get it out of their system. But they have do do something because people often use an online space designed for one activity for another.