Here is an interesting story I picked up from our local paper. In a nutshell, it pretty much says what many of us have said about modern Democrats. Most people agree with their policies on economics, foreign relations, and the like. Where most folks disagree with their party line is on "moral" issues. Traditional family values, religion, gay rights (specifically same-sex marriage), abortion, and stuff like that. According to this study, moral issues so outweigh everything else, and they so very mush disagree with the Democratic platform on such, that that has been enough to drive them away from the party.
Speaking personally, that is precisely what drove me away years ago. I do still agree with most of their platform. There are, however, some absolutes in my life, in my beliefs, that I will never compromise on for anything. The modern Democratic party has crossed the line on damn near every one of them. It looks like lots of folks feel the same way.
http://www.heraldnet.com/stories/05/08/11/100wir_democrats001.cfm