Right, I meant "no other site" at HN's scale. I tried to make that clear later (edit: and have added something earlier in the post to say it explicitly).
Of course I may be wrong about this—I probably am. But in that case I'm curious to know what they are, so we can learn from them.
It isn't just about scale, but also scope. If a forum has a specific topic—Lego, let's say—then the problems I'm writing about are off the table, because it's easy to tell which posts are about Lego and which aren't, and the community will happily support moderation of the latter.
> no other site is even trying to do this
many websites are designed this way. Really, think about it. Segregation doesn't happen automagically. Now, you could ask "but are the user bases as large as HN"? A few are and other aren't, I'm sure.
> it isn't like John Lennon's 'Imagine'
In the Anarchistic vision of 'Imagine', you would probably have a lot of HN-style arguments too, but they don't devolve into inter-national or inter-faith wars. When the "world lives as one", it's just like you describe - a lot of friction and discomfort but no segregation of hostile factions.
Finally, we need to remember that the level of hostility on HN right now is a lot for some people regardless of what they're used to. That doesn't mean we need to censor ourselves, but just to be aware that many people are more conflict-averse than the typical HN reader - and this aversion may well be correlated with, say, gender. So problems remain despite the positive view that you justly present.