It's not actually "vanishing" civility. Life has always been that way among those who live above subsistence levels. Court life in the middle ages is rife with examples. It's important to realize that these "jerks", "bozos", and "assholes" are all engaged in political maneuvering. They're playing an entirely different game than you, and the only way to stop them is to remove possible political reward for such actions, or at least raise the risks so high as to not be worth the effort to begin with.

HN has largely been successful in this endeavor through a mix of technology and culture. You can't get rid of it entirely, but you can certainly subdue it.