“If everyone in the world were homosexual, the human race would die out.” Or as Kenneth Minogue — not ordinarily a lazy thinker — recently put it:
If one’s notion of responsibility includes a concern with the continuance of our civilization, then there is a clear conflict between such responsibility and the advancing of homosexuality as an equally valid sexual option to heterosexuality. (The Servile Mind: How Democracy Erodes the Moral Life, p 310.)
Wordier, but I think effectively the same. As it’s been pointed out, this is a lousy argument. The refutation? If everyone in the world sought a cure for cancer, there would be no food, and the human race would die out too.
Arguments like these ought to be embarrassing, but for some reason they’re not. They are a scathing indictment of dentists, accountants, musicians, teachers, and basically everyone except subsistence farmers and hunter-gatherers. Only they pass the (apparently, I guess, sorta) Kantian test. If everyone in the world were moral philosophers, the human race would die out, and of this I feel increasingly confident.
You want a maxim to universalize? Find someone you can really love, body and soul. Commit to that person. Consider having children, if your biology and personal situation allows it. Even if the biology fails you, consider adopting.
But then gay and straight people would have to share a moral maxim. And there would be cooties on it.