Earlier quoted context omitted.
It sounds like a insurmountable problem. What makes this even more interesting to me is that HN seems to have this working pretty well. I wonder how much of it has to do with clear guidelines of what should be valued and what shouldn't and having a community that buys in to that. For example one learns quickly that Reddit-style humor comments are frowned upon because the community enforces it with downvotes and frequ…
I suspect HN succeeds due to heavy moderation, explicit community guidelines and a narrow topic set.
This may be a lot easier in places where there's an explicit point to discussion beyond the discussion itself - StackOverflow is another non-Reddit example. It's easier to tell people their behavior is unconstructive when it's clearly not contributing to the goal. HN's thing may just be to declare a particular type of conversation to be the goal.