I do not feel that gay marriage is a immoral issue. I believe that instances in the Bible that speak against it have been misinterpreted over the years. For instance, What Paul talks about in Romans (I think) deals with more of a social structure than anything to do with sexuality. In fact, the term homosexuality was not even existent back during these days. It is known through Roman writings and other archaeological information that gay couples were indeed fluent and accepted amongst the society as long as one came from more of a dominant family and one came from more of a submissive family. The issue of Sodom and Gomorrah deals more with gang rape than any issue of sexuality. I think it simply comes down to the fact that people fear what they do not know, and label it as sin, the devil, you name it. I am studying to be a counselor in a local seminary and I assure you that gay marriage will NOT bring forth famine, pestilence, earthquakes and the anti-christ. If you study history a bit, the same things were being said over the ending of slavery, women gaining the right to vote and desegregation. Face it, there are people, Christians included, that live their lives against things that are stated in the Bible (if you interpret those things literally.) Plus, you go Old Testament and we shouldn't even be playing football...
I think sometimes common sense needs to be applied in studying spiritual truths. I think a monogamous relationship, no matter what two individuals are involved, is a beautiful and highly spiritual experience. For those who are stuck on literal intepretations of the the Bible, I would simply bring up something that Jesus said himself: "Think not that I have come to destroy the law and the prophets. I have not come to destroy, but to fulfill." Just think about it.
The "devil" is not in those that think and act differently than us. The "devil" is the fear we have in those that think and act differently than us.