The observation that the internet breeds impoliteness is an old one, and I don't intend to repeat it. I would just like to point out that there is something concrete you can do, which I'm trying to do more often.
Most people don't make death threats, but I feel pretty comfortable saying that most people's contribution to the Internet is a net negative for civility. We tend to post only to point out errors, to "correct" "mistakes", to explain to somebody in detail why they not only believe the wrong thing, but are stupid for believing it. Greivance Law 3 usually kicks in for at least two people, and cascading insults are a normal occurrence on the Internet.