I wouldn’t be so quick to condemn this idea. Marriage is a religious institution first and foremost. Really, who cares what the state does with it’s (more and more) completely unrelated institution that goes by the same name.
Good point. And then it will allow for the union of a man and a dog, a man and three small children, a women and four goats, ten men and forty two lemurs, two children and their pit bull, and...
Really, we care. Every state, apart from what it might be argued theoretically, has always relied upon some kind of world view system of morality. Whether that was the pagan view of Rome, or in the case of the US, in the biblical view of Judeo-Christian propriety.
We cannot escape such a connection between the underlying world view and the public morality, so the question will be: With what do we replace this with now?
You should care! Children will be taught about homosexuality in schools. The rights of people who believe marriage means a man and a woman will no longer matter. We’ll have to accept gay marriage whether we like it or not. And this is just the beginning of the fallout. In Canada, the slip down the slope has led to a proposal to legalize polygamy. In Massachusetts, where gay marriage is already legal, there is a movement to reduce the punishment for bestiality. And it all began with legalizing gay marriage.
The problem is that the state does have an interest in promoting stable families with a mother and a father for the upbringing of children.