Earlier quoted context omitted.
And William Shockley with eugenics
Eugenics are "merely" deeply political incorrect/blasphemic/unethical, but not a wrong crackpot theory per se. Obviously what works for plants and animals would work for humans too.
For example, people do not use the term "eugenics" to describe the unintentional selective breeding of humans who maintain the childhood ability to produce lactase and thus can digest milk as an adult.
The term is also tainted by a long history of proponents and advocates wanting to apply the principles of selective breeding to non-inheritable traits, like "criminals", due to a naive understanding of genetics (eg, https://en.wikipedia.org/wiki/Eugenics#Objections_to_scienti...).
The phrase "what works for plants and animals" seems to be hiding a lot under the covers, like the number of gene lines killed off because they weren't profitable enough for the people doing the breeding. Even in domesticated plants there is an ongoing debate about decline and extinction of heirloom/landrace varieties, and consequential loss of genetic diversity, in the face of "what works" for industrialized agriculture in short-term/decade time-scales.
The "new eugenics" movement emphasizes how choice should be left to the parents, as an alternative to the history of the state deciding these matters. However, if we really are looking at "what works for plants and animals", we can see that optimizing for an individual doesn't always result in what benefits the group.
For example, you can breed an aggressive chicken, more willing to attack other chickens and take their food. The aggressive chicken will be bigger and heavier than the others, but if they are all that aggressive then they end up fighting each other, to the overall detriment of all.
Some of these options will result in a Prisoner's Dilemma, where if some parents choose trait X for their children than those children benefit (as defined by both the parents and children), but if all parents choose X then things becomes worse (again, as defined by both the parents and children.)
Which leads us back to how politics and ethics are inherently connected to the "eu-"/"good" in the deliberate selective breeding of humans, and not simply "merely" connected.