It's the reflex reaction of true believers of a rubber science. By pointing out the rubbery nature of their rubber science, you are "impeach[ing] the credibility of modern science"!! In 1930, Pope Piux XI condemned all the causes dear to the eugenicists, as any decent human should, Pope or not, Catholic or otherwise. The reaction then was the same reaction now. This is from Eugenics Review 23 (1931)...
"... the Pope delivers an uncompromising ultimatum not only to eugenists, but to all who seek to order their own affairs in the light of science and human judgement. It is a defiant return to mediaevalism... at the beginning of this survey it was written advisedly that the Encyclical was a return to the Middle Ages. Its mediaevalism is carried so far as to ignore all anthropology, all history not contained in Genesis, and to attack not only the practice of eugenics, but also the underlying biological bases. Not only is current biology specifically attacked, but an onslaught is made on the whole texture of science and the liberty of thought...Tap the knee, it jerks.
Evolutionists don’t buy into eugenics, because science has shown that intelligence is largely the result of training rather than genes.
And they don’t buy into racism, because science has shown that there are no biological human races. (there is more variation within any “race” you might want to define than there is between any of them)
However, creationism is still ripe for eugenics and racism. As late as the 1990s, creationist master Henry Morris was writing that blacks were spiritually and mentally inferior to other people.
Not that all creationists are racists; many would be horrified to find out the sort of thinking on which YE creationism is based. But it’s one of the big differences between science and creationism.