This happens on many sites, and in many cases I'd attribute it less to a reduction in "quality," and more to a decrease in homogeneity: a successful site attracts more people, with increasingly disparate backgrounds.
For the original users, who were charmed by the fact that "everybody has (more or less) the right opinion, and we can discuss rather than argue!" this can be a shock, but I'd venture that it's often actually a rather healthy thing, even if you unfortunately also get more trolls and flamers along the way. Pleasant as it is to talk with one's close peers, one can often learn more by talking to people one disagrees with...
It can go bad, of course, but HN certainly doesn't seem to show the usual symptoms of an internet cesspool; based on my short time on HN (~1 year), the S/N ratio isn't bad at all.
For the original users, who were charmed by the fact that "everybody has (more or less) the right opinion, and we can discuss rather than argue!" this can be a shock, but I'd venture that it's often actually a rather healthy thing, even if you unfortunately also get more trolls and flamers along the way. Pleasant as it is to talk with one's close peers, one can often learn more by talking to people one disagrees with...
It can go bad, of course, but HN certainly doesn't seem to show the usual symptoms of an internet cesspool; based on my short time on HN (~1 year), the S/N ratio isn't bad at all.