What do you mean by legitimate? I think you're just frustrated that thoughtful moderation is labor-intensive, and civility doesn't scale too well.

But at any rate, haven't you undermined your own argument? You've found the community of HN is right enough for you.

Anyway, I find your argument interesting nonetheless, especially if we substitute the word "country" for "subreddit" and so on. A country can be ruled illegitimately by dictator(s), and yet, if you can choose to switch, switching arguably may be a legitimate strategy or solution.