I'll start by saying this is a tough issue. I'll also say that old_tony is not the only one against this ruling, and raise my hand. I'm willing to bet there are others, too, who won't do so because it wouldn't be politically correct, or the nice thing to do.
Beyond faith-based reasons, though, I think there is a general issue that's being confronted about a lot of things, and that that is part of the problem. That is, people seem to not have much problem with anything anymore. Or else they say, too easily, that they don't. That, in my opinion, is a problem.
A person's stance against same-sex marriage may not have much actual impact on their life. Heck, I suspect that's what drives a lot of people's stance for it. They do not know, interact with, or deal closely with many who live that lifestyle, and so, basically, who cares, right? It doesn't make any difference to me so...it doesn't make any difference to me.
But a person still doesn't have to like this. It can be that they just don't, and that that influences their beliefs.
I'll use myself as an example. I am Christian but I'm not sure my disdain for this ruling even comes from that, really. I just know that I struggle with seeing men kiss men and women kiss women in any more than a peck-on-the-cheek way. I don't like it. It bothers me, and I can't give any reason other than the fact that it just seems wrong. It just does, in much the same way as polygamy or bestiality (which, I noticed, people have not addressed).
To me, it's just...wrong, and the fact that anybody, or everybody, else does not think the same way doesn't change anything. And being against one thing doesn't necessarily mean I am against something else, i.e. outofplace's argument that being against same-sex marriage means I have to be against voting for women.
It's just not so. People really can have one opinion about something, and also have another opinion about another thing. Not everything necessarily means the same thing to a person, or moves them as much, or as much in the same direction. It just doesn't.