I think the reason why Hacker News works is because the demographic are not all the same - there are all kinds of people that are active on the site, rather tha

I think the reason why Hacker News works is because the demographic are not all the same - there are all kinds of people that are active on the site, rather than simply "friends of x" and "friends of friends of x" which often leads to inane comments like the examples you listed. I don't think one can engineer this collision of demographics, I doubt the design nor even content allows you to control it once the wheels are in motion.