None of my objections depends on interpreting “natural” as meaning what happens in the wilderness, so that point of yours strawmans the article. If you’d rather explain human nature in metaphysical terms of “essences” or “forms” rather than evolved adaptations, the objections can easily be reformulated in those terms.
Natural moral law theory would still commit the naturalistic fallacy of inferring values from facts, and this theory would still conflict with the Christian original sin doctrine since human nature specifically would be tainted. And this account of morality would still be subject to arbitrary conservative biases since the Catholic would include or exclude traits based on such prejudices.
Take your example of sexuality. Sexual reproduction did indeed evolve as a fitter way of transmitting genes, compared to asexual reproduction. That’s sex’s biological function. Alas, it’s fallacious to infer that what’s biologically functional is automatically morally obligatory. That’s the conservative’s naturalistic fallacy.
You see this crop up in your moving of the goal posts from morality to the weaker concept of “normativity.” It’s normative for hearts to pump blood or for wings to enable birds to fly, but that doesn’t mean those traits are good in a moral sense. As I said in the article, it’s normal and normative for humans to proceed from many cognitive biases that evolved to help us make snap decisions in a wild environment. Now that we live in artificial environments, those traits are no longer optimal, and our interests have changed and shifted the moral discourse.
Is “the nature of sex” confined to what biologists say about it? Here we see the conservative’s bias creeping in to shape something’s so-called metaphysical essence. Biologists tell us about biological functions, but only social Darwinians think there’s nothing more to morality that those functions, purposes, or “final causes.” Animals are content with those functions, but not people because what’s crucial to our nature or essence is our autonomy, our ability to define ourselves largely by improving our environment and by adapting to human cultural standards. Evolution has one set of priorities whereas our species has another set, and it’s fallacious to equate them without good reason.
I said in the article that both heterosexuality and homosexuality are found in nature, but I didn’t say that they’re both therefore functional and normative in a biological sense, let alone that they’re both moral. On the contrary, I said that because nature is amoral, natural norms or forms don’t entail moral obligations. Animals follow their nature not because they’re saintly in being themselves but because they have no choice. People have a choice, and that’s what opens moral questions for us. Should we follow a primitive level of our nature, such as by submitting to racist or sexist prejudices in the “traditional” manner? Notice how saints frequently renounce their sexual nature, aiming for a higher kind of morality than deferring to some lazy, biased conception of their form, essence, of nature.
