What a question.
Marriage is between two people and their SAOTU, not government. That's not to say that government doesn't legislate morals. They do.
But why does marriage require a license? Ultimately, it's for the sake of the children. It's society's way of saying, "hey, your child is a legal responsibility" and "we care about the welfare of the children." I can't find any concrete evidence to say that homosexuals can't provide as loving and moral of home as heterosexuals. I imagine most fear comes from the idea of relaxing laws on marriage means a relaxing of care for children. Obviously, that's not the statement anyone wants to put out. But this doesn't seem like a relaxing of laws, just a broader definition.
I shrug my shoulders and try to answer the question why not? Can it make things worse?
In another light, this seems to be an issue like drinking. Right, wrong, or indifferent, drinking is regulated. Oh sure, it's legal, but some find it immoral, others find it moral in moderation, and others use it as a powerful drug leading to alcoholism.
Well, homosexuality is considered immoral by many for the the same reasons as drinking. It could promote the idea that homosexuality is OK, and predispose children to homosexuality, and others see it as an escape into self indulgence. Frankly, I find these arguments hogwash.
But I don't have the whole issue sorted out in my head. It's obviously unnatural in that our bodies weren't made for homosexuality. But we poke holes in our ears, tattoo our bodies, and other things that aren't natural.
Until someone shows me how legalized homosexual marriage is bad for society, I won't be anti.