I don't know of many evangelicals who want to deny gay couples their legal rights. However, most of us don't want to call it marriage, because we think that word has religious connotations, and we're not ready to see it used in ways that offend us.
I think there are other issues that the Democrats could use to rally evangelicals. There are a lot of us, for instance, who believe that the Bible calls us to be environmentally responsible.
Relegating women to second-class citizenship was abolished when Jesus died on the cross.
There is no doubt that religion had already waned under the onslaught of the Enlightenment, but it was Freud who provided the radically new understanding of human nature that made any religious explanation of the whats and whys of our personhood seem naive.