Because none of the Democratic candidates suck. No. really. Despite what you've heard from various people around this place lately, none of the "Democrats" is really a Republican, none of them are Bush-lite, and none of them killed your mother and then hid her body. That evil, centrist Hillary Clinton has a Progressive Punch Score of 91%, good for 16th in the whole senate. And that noted hater of labor, Barack Obama, has excellent ratings from labor organizations. Joe Biden, despite an unfortunate tendency to open mouth and insert foot, has been the best critic of the Republican field. Dennis Kucinich, for all of his quirks, is the most uncompromisingly liberal voice in the race. Chris Dodd has been the loudest voice in the whole field on civil liberties issues. And John Edwards, well, read pretty much any diary on this site to find out why people like John Edwards.
So, seriously, there really isn't an obviously wrong choice in this cycle. There is no Zell Miller or Joe Lieberman running for president (Want proof? Lieberman had to back a Republican to find a candidate who was in line with his views). Vote for who you want. The only wrong answer is to get so miffed that your candidate lost that you don't throw your weight behind whoever emerges the victor.
And this is a message to some of the more zealous supporters of various candidates as well; if you truly believe that Barack Obama, or Hillary Clinton, or John Edwards, or any other candidate is a Republican in disguise, then you need to take a major step back. For a few months now, bloggers like Matt Yglesias and Ezra Klein have been pointing out how the primary process tends to turn molehills into mountains. It takes minor policy disagreements within the parties and turn them into blood feuds, while downplaying the truly immense differences that exist between the two parties. Thus, the Democratic debate on health care is "should we have mandates or not?", rather than "is Universal Health Care a good idea". The debate on Iraq is "how quickly can we safely withdraw troops" rather than "how many more troops do we need to send to win?" The debate on Social Security is "what is the best way to shore up the program" rather than "what is the best way to destroy it?"
I'll be frank, if you are incapable of recognizing that every candidate on the Democratic side shares the same core principles, and that every candidate on the Republican side opposes them (or at least pretends to), then you're a part of the problem. If you can't separate "I like candidate X" from "I must hate candidate Y", then you're a part of the problem. If you truly believe that someone is a bad Democrat for supporting a different candidate in the primaries, then you're a part of the problem. And frankly, the rest of us find your self-righteousness, really, really dull. We've spent 7 years now dealing with a leader who has total conviction and zealous certainty in everything he believes, and who demonizes anyone who thinks differently. And it's sucked a lot.
If you think "Candidate x is the best choice for America" means "candidate X is the only choice for America, and anyone who disagrees with me must be destroyed (or just annoyed for 6 hours on the internet)", then it's time for you to grow up. Because there's going to be a nominee, and the chances are it won't be your candidate. That's something you're going to have to get past, or, God Jed, I don't even want to know you.