> there's a far more positive community when people have a shared interest

Even old fashioned web forums and email listservs are still thriving in some niches and work this way.

I think reddit fails here because it's too frictionless. Requiring a little bit of intentional action to join or subscribe keeps out a surprising amount of drive-by trolls.

HN is pretty big now and has its share of trolls and bots but because it doesn't use social media accounts it's not nearly as bad as Facebook or Reddit.

> It seems like social networks that stay small and focused can maintain a fun and productive environment that degrades over time in larger networks

I would love to find some good social networks for myself but discovering them is hard and I don't have the free time to dig like I used to to find the hidden gems