It's not even that there's a lack of solidarity, the majority of the country didn't want this to happen.... it's just that one side of the issue is far more united (and issue driven) than the other.
Put another way, there are far more people who vote purely on conservative culture issues than liberal ones.
I hate single issue voting as much as the next guy, but that's probably what it takes to actually match or exceed the intensity of the other side of this issue. Sad to say, but it's the reality.