Aristotle taught that everything has a purpose, its “final cause.” Things are moral if, and only if, they serve this final purpose. Adapted by Aquinas, this idea of ethics became Christian “natural law.”
Let’s talk about sex, as natural law theorists inevitably do. If the final cause of sex is reproduction, say the Catholics, then sexual relationships are only moral if they have this end in mind. Thus, for example, contraception is immoral.
What, from a Mormon point of view, is the final cause of sex? And if we can determine this, how might this help define what sexual expressions are moral, and which are immoral?
According to Mormons, sex is for reproduction and to strengthen the relationship between husband and wife. But these are, perhaps, only efficient causes, the means by which one attains the final cause. In this case, the final cause is eternal marriage and increase. Thus anything that detracts from this final cause is immoral. What one reasons to be such a detraction is, of course, open for discussion.
Might natural law be helpful in questions of Mormon ethics? I would tend to think so. To quote the great Nathan B. Oman re: SSM: “It seems to me that any Mormon discussion of same-sex unions should quit mucking around with Sodom and Gomorrah, the Mosiac law, or the New Testament. The real issue is what does one do with sections 131 and 132 of the Doctrine and Covenants. These are the sections that link the concept of exaltation with the concept of marriage.”
The church opposes SSM because of what it understands the final cause of sex and marriage — and the road that leads to it — to be. That is where the true debate lies. Demonstrate how SSM does not detract from the final cause of sex and marriage in Mormon theology, and you’d have something interesting. “Mormons are homophobes,” isn’t good enough.
For their part, Mormons need to explain why SSM so gravely undermines the final cause that it requires the intervention of the secular state to stop it.