It is a well-known phenomenon that people will write all kinds of rude and nasty things to other people on the internet under the cloak of anonymity, things they wouldn't dare to say to people to their faces. This is especially true in political disagreements on public forums between Democrats and Republicans.
Recently, however, the Democrats have been spewing the venom at each other, as the partisans of Barack Obama and Hillary Clinton have become bitterly polarized against each other. I've read a few postings on left-wing web sites, and it's obvious that the two groups just plain don't like each other. There's a lot of talk in both camps about how if their candidate is not the nominee, they won't support the other candidate in the general election. For most of them, it's probably just talk; however, a certain percentage may feel so angry about the primary campaign results that they may vote for Ralph Nader, stay home and not vote at all, or even vote for John McCain.
The problem the Democrats have is that they have two candidates whose supporters believe that if their candidate doesn't win the nomination that it will have been "stolen" from them, and they are taking it very personally. Combine this with Democrats talking to each other the way that they normally talk to Republicans (i.e., insults, personal attacks and trash talk) and it's no surprise that so many of them detest the supporters of the other campaign -- and by extension, the other candidate as well.
Finally, there's a story in the news about left-wing Air America radio host Randi Rhodes being suspended for obscene remarks she made at a comedy club in San Francisco about Geraldine Ferraro and Hillary Clinton. I'm no supporter of either of Ferraro or Clinton, but Rhodes' vile remarks (Warning: NSFW!) were beyond the pale. When you have a Democrat like Rhodes using terms like "f***ing whores" to describe two of the leading women in her own party, you know that the Democrats' uncivil war is taking its toll. When there's that much bile and venom between the Obama and Clinton partisans, it's unrealistic to expect that they will all join hands and sing "Kumbayah" when the nominee is decided.