The reason why so many Christians are opposed to gay marriage is that marriage is a picture of God's relationship to the church. (to them, us) a marriage between two people of the same sex is a perversion (for lack of a better word) of that picture. Not saying that we should or shouldn't legislate our religion, but as you can see that is why there is so much opposition to it. Please don't go there with, divorce rate of Christians. No church condones divorce rates at these levels.
My personal opinion was, that all unions should be domestic unions under the law. If you want a marriage (the religious institution) then go to your church and get it. However, of lately, with all the "your a hater" and "if you have that opinion, keep it to yourself" the gay marriage crowd has shown themselves to be nothing but fascists and thought police. So, they lost some of the sympathy they once had with me. It's clear that this campaign is an assault on religion in general and has less to do with Mary and Debbie or Bill and Bob wanting Tom share their lives together.
First of all, I gotta disagree with your first statement. Some people like to draw this comparison between marriage and God's relationship with his church, but I have always found it totally irrelevant. I don't see how a religious ritual whose aim is to deliver God's blessing upon a couple (two people) could validly represent the relationship between the Creator and his creatures. You also say "if you want a marriage (the religious institution) then go to your church and get it", but you see we have just established that is impossible because the majority of Christian churches will not celebrate gay marriage.
Also, when you say that it's pretty much a church's right to decide the rules that its members should follow I think you are forgetting that "the church" is not just a board made up of a small number of people sitting around a table getting to pick which rules the whole religious community should follow. "That church" is actually made of of ALL the believers, and since there are loads of gay christian believers who would like to get married they should have a say too in the debate, not just outside of the church, but within the church, if they are active members of that church. I don't believe it's fair to just tell these people "well then you are free to choose another church if you don't find this convenient", because those people might as well be as fervent believers as any other straight member, perhaps even more.
Personally I didn't have a problem leaving the catholic church when I realised that the majority of them 'disliked' gay couples, as I don't necessarily see them as the only representation on earth of my God/faith, but I appreciate that other Catholics might not be able to do the same, and it is extremely cruel to leave these people with the only option to either live lonely for the rest of their lives or leave their religious community, without even trying to have a debate with them first.
The problem with organised religions is that they have become too much like authoritarian institutions, where someone writes the rules down and everyone else must obey. The people in the clergy forget that, last time I checked, there were no angelic creatures or divinities among them, therefore, since we are all human here, a lay believer has got just as much say on dogmatic issues as a priest, and a simple priest has got just as much say as the pope/ the archbishop of Canterbury (delete as applicable), and my interpretation of the bible could be just as valid as pope Francis'. So ultimately who are they to impose their own interpretation of the scriptures on everyone else and sell it as 'the Truth' and then use it to say that "Our church does not allow gay marriage, if you want that get a civil version of it".
