What part of social liberalism has anything to do with logic? The democrat platform is based largely on emotional arguments and opposition to what the "other side" is doing. Radical democrats and radical republicans are running the same ticket, namely making others do what they "feel" is right, based on their emotions and faith.
The trick is, nobody gets motivated by common sense and moderation anymore so political candidates must either be FOR some extreme set of values, or AGAINST whatever it is their opponent stands FOR. As the republican fringes tend to try to claim some sort of moral high ground based on religion, it's quite natural for their democrat opponents to swing full-scale the opposite direction. Republican radicals want to ban gay marriage? Then a gay candidate is the obvious democrat choice because if the democrat was FOR something, then the republicans would use their moral pretense as a way of justifying being AGAINST whatever it was the democrat was FOR.
I'd like to see a candidate that actually had a plan. Reagan had a plan... That was cool, and he changed the world. Even Bill Clinton had a plan. The problem with Bill Clinton's plan was that it changed based on the daily polls, so it wasn't really his plan and he had a tough time following through with anything because he kept abandoning his causes whenever he sensed resistance.
Right now, it's cool to be against whatever it the President does so a political candidate can gain an immediate boost in popularity by being the opposite of the President. That will only go so far, and eventually the candidate will have to either come out FOR something, or successfully sell the message that their opponent is a terrible person and they are not equally terrible. That's the trap the democrats seem to have been falling into... They're great at being against stuff but have had problems coming up with positive themes and positions that aren't based entirely on interfering with everyone's life based on the emotional issues of one small group or another.
That's why the religious right hasn't taken hold of the country... Their position is pretty much based on the idea that they should be able to tell people what they can or can not do, and that pisses off a lot of people.