Two arguments against the recognition of same-sex marriage are: 1. that it goes against the tradition that marriage is between one man and one woman; and 2. that homosexual sex is contrary to natural moral law. Neither argument is trifling. The second argument– that homosexual sex is contrary to natural moral law– is the one that so-called “conservatives” need to trace more finely.
If they did trace it more finely, it would go something like this: Humanity has a special relationship to God. God is our Creator; we are God’s creatures. Our purpose on Earth is to praise and glorify God, which means to show forth– in thought, word, and deed– the divine image in which we are made, and to manifest the life of God in our lives. One of God’s most powerful attributes is that God creates; God brings forth life– in a profound way, God’s very essence is Life itself. Therefore, to create– and especially to create life– is a sacred power in the human being, precisely because of its closeness to God’s own creating, creative nature. Homosexual sex is against natural moral law because such sex does not– cannot– produce life, and is therefore contrary to humanity’s purpose in life– which, again, is to manifest the life of God in our lives. (Please bear in mind that I am not owning this argument. I am merely setting it forth).
Most conservative arguments against same-sex marriage stop at moralizing (heterosexual sex is good; homosexual sex is bad– it says so in the Bible), and don’t reveal the moral and theological reasoning behind the conclusion. Liberals are rightly critical this kind of peremptory moral judgment.
For their part, liberals have largely failed to engage the questions that this strong version of the conservative argument raises, namely, What is humanity’s relationship to God?; and How does sexuality relate to the purpose of human life?