The problem with "eugenics" as it was at the time, is that absent the discovery of DNA and the "genetic code" the whole bit was based on phenotypes and moonshine. OTL we can isolate a large number of specific genes that cause specific problems, of course we can't yet map things like intelligence, longevity (as opposed to causes of decreased lifespan), athletic ability and so forth which are more complex than point mutations. All that is before the "racial" elements of eugenics were tossed in.