[palata]

I think good communities exist, but it's not necessarily easy to find them. Some comment here mentions USENET, and I think it was from a different time, where there was a very strong filter based on who joins Internet communities (only a specific subset of people were doing that). Now pretty much everyone does. It's probably easy to find a community of Taylor Swift's fans because there are so many, harder to find a niche community.

The hard thing, IMO, is that it's also very hard to promote those communities to the people who would fit. If a community is over-advertised, then many people will join and alter it, maybe destroying it (say you have this nice community of mobile development that talks about Kotlin and Swift, and in a few weeks you get 3000% more users who all love PWAs... it won't be the same community anymore).

One could hope that algorithms would be very good at creating perfect communities of people who match with each other, but it's hard to say from history that social networks are good at that except for a few examples were they actually grouped together people with pretty radical opinions and it was not exactly great.