Obviously, laws affect society. To assert otherwise is to demonstrate one's own insanity, and besides, it's self-defeating. If laws don't change society, then whatever change you are arguing for in the law is ultimately irrelevant, so you should basically drop it. But of course, they do change society, and everybody knows it.

Anyway, I think redefining "marriage" to include pairs of people whose relationship has nothing whatsoever to do with procreation, whether in form or in function, will have unforeseen social consequences. I think it will be a short road to polygamy and to denying children up for adoption their need to have a mother and a father. That is one reason among many I'm against it. However, I sometimes find it ironic that Christians are far, far more vocal in opposing gay marriage than they are in opposing no-fault divorce, the lack of civil penalties for adultery, and the deinstitution of common-law marriage. You'll notice that in the Torah, God's laws for his people about marriage weren't "Marriage is just for a man and a woman. Otherwise, do what you want." There were lots of regulations designed to protect marriage and the family. Do many Christians today advocate laws that actually protect marriage?