Anybody who says the Bible defines marriage as something only between a man and a woman is either ignorant or a liar.
I may not be the world's greatest expert on the Bible, but I can read as good as the next girl. And sometimes I do. So let me tell all of you that the Bible don't say nowhere that marriage is between a man and a woman. Check out your King James if you don't believe me. Now, there's lots of references about marriage in the index, but they're just about divorce and adultery, not defining which marriage partners are permissible and which aren't. And some of that stuff about divorce and adultery makes me doubt that the Bible is really the word of an Almighty God and not a translation by a mean-spirited husband. But whichever way you read it, the Bible says not one place that marriage can only be between a man and a woman. No place, no where, no how. Zilch.
Me, if I was gonna bother with a law to keep people I didn't approve of from getting married, I'd put in anybody who abused a child, anybody who poisoned the environment knowingly, and everybody who drives on the shoulder because they don't like waiting in traffic with the rest of us.