1. Eliminate anonymity. Make people liable for what they say and do. And don't tell me it infringes on your privacy; the marketers and the government are already tracking everything you do; don't kid yourself about that.
2. Remove "Comments" sections from news articles, particularly on the so-called "respectable" sites. Letters to the editor are a time-honored tradition, but snide remarks from every Tom, Dick and Harry with a keyboard only serve to distract. Let people employ their first-amendment rights on their own forum. Employ ruthless moderation and provide trackback links to worthy dissenting viewpoints.
3. Stop reposting other people's snotty propaganda on social networking sites. It's simplistic, it's annoying, and it helps nothing. People who agree with you will just stroke your ego. People who don't, will raise your blood pressure. Any sentiment that can be expressed in a bumper-sticker is probably over-simplified anyway.