The issue, prarie girl, is basically the religious and societial concept that marriage is a union between a man and a woman, under God. There may just be more people in the U.S. who believe this and also who feel it is something vital to protect. I disagree, but no man is an island- we are all, more or less, subject to the ideas, beliefs, and dogmas of the societies we live in.
I am not totally sure how I feel about homosexuality, even though I am in favor for gay marriage. Its not easy for everyone, for a lot of people homosexuality isn't an easy concept to grasp and it threatens what people believe about things. This causes a hostile response. I'm not saying this to be hostile towards you in the least- I just think that until people take time to understand both sides of an argument and be open minded in that way, positive solutions/understandings will be difficult to come by.