And as for more public forums like chat and perhaps reddit like topics with replies, they would be pretty dead without the random public people’s contributions. Three degree separation is pretty small across moderate to niche topics or chats.
Discussion
I did not say 3 degrees. Grow it as necessary but keep it "invite only". If new accounts with zero follows can make it into your experience, you're open to spam. If you see only the "closest" 1 million authors, you should be almost spam free.
My LinkedIn is filled with effectively bot accounts. They seem real, but it’s low grade and all within three degrees. And they look like real enough, at follow or accept connection point I have no way to really know. And worse, I have colleagues who accepted them and make them seem more legit.
That's where I need a negative signal, too. Public block lists, ways to disregard somebody's follows or only consider the first 100 follows each, etc.