Right. Which simply means that if homosexuality does have a genetic basis it is not for homosexuality qua homosexuality – ergo there is no “gay gene.” Again, one of the current popular explanatory theories of homosexuality states that homosexual men improperly inherit a genetic disposition from their mothers to seek out and enjoy lots of sex with men. This also explains the statistically-observed finding that homosexual men tend to have substantially larger families on their mothers’ side than their fathers’ side. Obviously it is evolutionarily advantageous for women to possess this trait (since it will dispose them to reproduce) and extremely disadvantageous for men to possess it. But if the advantage for women is greater than the disadvantage for men, then the trait will continue to persist in the population, even as homosexuals themselves go extinct every generation.
After all, suppose a woman who has this trait has 5 kids instead of the normal 2. Of those 5 kids, one winds up gay. She’s still having twice as many kids who will reproduce as the average person: therefore her traits propound in the population even though the one kid in whom this trait manifested improperly almost certainly won’t reproduce.
Well, that’s an assertion, not an argument. The Catholic Church uses “disorder” to mean, literally, contrary to the normative order. I don’t think there can be any argument that sexual complementary is the normative order. That some people’s impulses don’t line up with that normative order doesn’t prove there’s no normative order, it only proves that, for whatever reason, that order does not prevail uniformly. (Only nearly-uniformly).