A practical example of this can be seen in lobsters invite system, where if too many of the invitee accounts post spam, the inviter is also banned.

And another practical observation is that not many people have Lobsters account or even heard about it due to that (way less than people who heard about HN). Their "solution" is to make newcomers beg for invites in some chat. Guess what would a motivated malicious actor would do any times required and a regular internet user won't bother? Yeah, that.

I think this is the inevitable reality for future FOSS. Github will be degraded, but any real development will be moved behind closed doors and invite only walls.