The highly developed practice of animal breeding is an obvious referent for the scientific validity of the enterprise, which has failed not on scientific but on ethical and moral grounds.
Animal husbandry proved, centuries before Darwin, that creatures can be bred to enhance useful traits. The problem with applying that logic to humans is, as you point out, a moral and ethical one: Useful to whom? Who decides? Any answer to those questions requires value judgments on inherently unscientific grounds.
The essential failure of eugenics as a legitimate science is that science is descriptive, not prescriptive. When you use physics to build something, you’re an engineer, not a physicist. If you use biology to practical ends, you’re a physician, not a biologist.
The issue is not that this or that experiment in Eugenics failed, but that it is inherently unscientific and immoral.
And it was entirely HETEROSEXUAL... imagine that...
"What's he that is not born of woman?"Macbeth. Act V, scene VII.