On the issue of gay rights, the Democrats have all become states-rights proponents. They are unified in this position, from frontrunners Kerry and Edwards to Chairman McAuliffe. On every other issue I can think of, big and small, the Democrat position is that federal law should override state sensibilities:
Gun control, abortion, environmental regulation, energy consumption, the drinking age, even seat belt use, have all been dictated in some manner to the states, and always at the behest of the Democratic party. Along comes gay marriage, which the far left supports enthusiastically, but the moderates and centrists oppose, and the Democratic party is too intellectually weak to take a stand one way or the other. So they say they oppose gay marriage, but favor "civil unions," and shrug that it's up to the states, so their position doesn't matter anyway. They have been thrown a political hot potato, and they don't want to touch it, so they are throwing it back at the states.
When John Kerry announced his candidacy, he stood before a sign reading "The courage to do what's right for America." He would do well to demonstrate what he meant by that.