Here's a recap of reasons why the Democrats don't deserve your love this year, from local San Francisco chap and Nader running mate Matt Gonzalez. Worth reading along with this explanation of his from a few months ago of why he isn't (and nobody should be) excited about Obama.
The article's title is "What do they have to do to lose your vote?", and I've found that that's a useful question. When I'm talking to an angry Democrat—filled with righteous fury at my ignorant, foolish, idealistic, naive refusal to go along with their chosen party—I'll sometimes ask: is there anything whatsoever the Democrats could do to lose your vote? Is there any policy so amoral, any strategy so calculating and unethical, any crime so odious that you'd feel you could no longer support them in good conscience?
If the answer is "no", you're dealing with a cultist and there's no point in continuing the conversation. But if the answer is "yes" you can say "I feel the same way, and they already have crossed the line for me"—and then proceed to explain why, calmly and rationally. Once you've established that you both accept the underlying principle, it's just a matter of degree. You probably won't convince them to desert the Democrats, of course, but you may well be able to turn them from condescendingly dismissing your position to understanding and even respecting it (even if they still disagree with it). And that's a critical first step.
[ This approach works more generally as well. Back in 2003 I went over to talk to a young vet counter-protesting at a massive anti-war really. He was probably expecting a shouting match, but I just talked calmly with him about why I was marching on the side I was on. He was skeptical of my account of US support for Saddam Hussein, the US betrayals of Iraqi Shiites and Kurds, the (intentional) effects of sanctions, and so on, which was fine—I agreed that he should check it out for himself rather than taking my word for it. But then I asked him: assuming solely for the sake of argument that the things I was saying were true, would he still be as comfortable about supporting the war? He didn't change his mind on the spot, of course, but he looked thoughtful, and when we were done talking we shook hands. I'll never know if it had a lasting effect, but for that moment at least I think he understood that we really did have good reasons for opposing the war. ]