Things that escape your notice because "history is boring".
Eugenics was a pseudoscience created before anyone even knew what DNA was, let alone understood. Eugenics goes as far back as Ancient History. Breed the "best" humans through various methods including infanticide.
Modern eugenics began with Francis Galton in Great Britain in the late 19th century. It quickly spread and was enthusiastically embraced in the U.S. where methods including forced sterilization and forced abortions were strongly encouraged. And employed.
The U.S. was a leading proponent of eugenics to the point that Hitler (yes, THAT Hitler) was inspired to further develop his own concept of a "master race". Hitler believed that the U.S. would approve of his plans. (Side note- antisemitism was widespread throughout Europe and quite common in the U.S. in the early 20th century.)
Imperial Japan had its own version of eugenics tied to its extraordinarily racist world view. Japanese soldiers considered Chinese and Koreans to be subhuman. Again I will point out that extremely racist national ideologies were very common. It does not excuse them. Obedience is not a virtue and it makes you complicit in any atrocity.
Racism is only a small part of eugenics. Classism and cultural arrogance play a role as well. "Scholars" of eugenics in the U.S. extended the notion of "undesirables traits that should be eliminated" to include anti-social behaviour, homosexuality, proponents of degenerate arts (Picasso was included in that category. Yeah.), opponents of government rule, people prone to depression or mania, unattractive people (Yes that standard is not objective at all) and they wanted to control the number of common laborers because yes they were needed, but if there were too many they might decide they don't care for being bred like livestock.
Anyone who sees the idea of removing undesirable genetic traits from the gene pool as just good common sense has no grap of history and is oblivious of the results that are inevitable under authoritarian rule. The definition of "undesirable" will be expanded. Oh, and also-the diminishment of genetic variation creates a sharp increase in the likelihood of mutations, good or bad, that will be inherited and passed down. Because you've narrowed down the diversity and if you've truly successfully done that, good luck breeding your way out of your mess.
