They don't? are you sure?
I support any policy that gives people equal legal rights. If you want to marry a man, a woman, 2 men, 2 women, a man and a woman at the same time, or whatever combination of the above. I don't see why you shouldn't be able to. As long as you obey the law, fulfill basic social obligations, and contribute to society.
I am very happy about this, it shows a great increase in understanding among Americans as a whole.