Screwtape, do you really think the Democrats passed things like the health care bill out of the goodness of their hearts?
To put it bluntly;
If the Republicans have as a major part of the stategy of staying in power of helping out the extremely rich, and the Democrats have as a major part of the stategy of staying in power of pleasing the general populace, and, I'm not part of the extremely rich, which of the two will more likely have a better result for me? Democrats.
Another major part of the of the stategy of staying in power for Republican is to please the Religious Right, and I'm not part of the religious right, and part of their interest would be to KILL
me, having them not in power is in my own interest.
Furthermore, I see the relative health of national economies that are capitalist with some socialist elements such as Germany or Denmark, and the horrible economies of purely capitalist societies like Somalia. The Democrats seem to be closer aligned with the former, and the Republican with the latter, it is in my best interest to vote Democrat.