I don't think it is quite as black and white as people seem to think it is. Just to note my biases in at the door so nobody misunderstands me. I am unilaterally for gay marriage, and I'm also pro-marriage in a church. However I think it is deeply unfortunate for the issue to be forced legally in this manner.
The Church, or any church for that manner is like a family, and like any family is not going to be perfect. Religion has had a hand in the oppression of women, destruction of other cultures, abuses committed against children the list goes on, but it has also contributed to great acts of kindness, charity, art, music, architecture in short an equally long list. It is in ultimately a reflection of us as humanity both good and bad.
Forcing action through the courts does not automatically shift the consciousness of the Church or even humanity for that matter in the right direction. Rather that the truth of the cause, standing on its own merits should and I believe will affect that change.
I can whilst I do not personally agree with it sympathise with the viewpoint that a marriage performed in a church symbolises the male/female relationship expressed with the purpose to create children. As such two men or two women are not through sexual union able create children.
I believe it is possible to hold that belief and not be against gay rights or homophobic in any way whatsoever. To lambast someone in that way over a point of their faith who has not expressed any hateful opinions (or actions) towards homosexuality betrays a lack of comprehension of the theological landscape surrounding this issue.
To people who do hold that view earnestly whilst I certainly do not speak for God in this matter please consider this: There is a comparable amount in the bible about not eating pigs as there is condeming homosexuality. In addition there is a lot written biblically that is of a practical rather than spiritual nature. The pig ban for example is good sense for its difficulty in keeping safe to consume in the environments in which it was written too.
Homosexuality I suspect goes hand in hand with the having multiple wives parts of the Old Testament. For a civilisation to thrive against its neighbours it needs numbers (for protection if nothing else) so making sure every possible potential mother got to bear children was vital, as was ensuring every male contributed too. Losing a valuable male to a same sex marriage would limit this (and I say valuable merely as a numerical expression as a great many more women reached sexual maturity in those times than males, hence taking multiple wives).
Now it's safe to say in modern times we don't need to ban pork, encourage men to take multiple wives, and in fact looking at the world with all of the overpopulation we should herald every homosexual as a potential blessing. If you believe God created us in his image, we were endowed with reason to figure out and apply ancient teachings sensibly, rather than holding on to what was common sense for life thousands of years ago, and embrace it out of blind obedience now. I appreciate you may believe this is wrong, but at least consider what I have said, I may well be wrong, and should one day I stand before my creator to be told I homosexuality is a sin, I will in all humility apologise and ask for forgiveness. However it was my attempt to follow the bedrocks of my faith namely love, and compassion that have led me to my conclusions.
On a final note marriage used to occur when two people consummated a relationship (we're talking the very early days of Christianity here). No churches or priests just an honest expression of love between two souls. Ceremonies in Churches came much later when primogeniture needed to be established once kings and such started to convert, and the priest became a witness to who was precisely married to who. So yes in a sense marriage as a ceremony may be about that, but in the eyes of God I believe a great many homosexual couples have been joined in love under his gaze. I hope for the day the whole humanity follows suit.