You cannot defend the idea that men and women are different with science—not consistently and effectively—because science itself is disintegrative, it breaks down through analysis. What starts as an eternal duality turns into charts that depict variations in hormones, genes, and so on; although these individual constituents aggregate into the familiar categories “man” and “woman” the duality has been blurred. The boundaries are fuzzy and, with help from technology, we can move from one category to another (become transgender).
It’s the same for race. Genetic research does not confirm races exist but rather undermines the concept “race”; if you take a genetic test, you find that you’re 48% English, 12% French, 2.2% Italian, and so on—again, there are aggregations that clump, as with biological sex, into “English” and so on but the damage has been done. Before, you said, “I’m British,” but now you’re 48% English and so on. You’re an aggregate and, as the left says, “Everyone’s just a mix anyway so it doesn’t matter”. At one level, genetics confirms sex and race as real but what it gives with one hand it takes away with another.
If you accept Darwinism, races change over time—in one direction or another—and so the Darwinian view destroys any notion that there is a “nationality”; everything is in flux—possibly we are evolving into sponges (perhaps the most sponge-like people have the most offspring that survive). To assert, from Darwinian thought, that some racial types should be bred is not a scientific proposition—it’s a value judgement beyond the facts; hence you end up back at a value judgement whether you have the scientific evidence or not. “This type should continue to subsist. I hold this type to be superior.” We live in scientific societies that are valueless; and the right really wants to assert values through science but cannot do so, and yet to navigate the world we need prior values if our actions are to make sense—hence metaphysics.