Sweden set up a eugenics plan, grounded in the science of racial biology, between 1934 and 1976. The first country in Europe to later abolish forced sterilisation was carrying out a policy under which between 20,000 and 33,000 Swedes were forced to be sterilised.
Victims were young and mostly female, judged to be ‘feeble-minded’, ‘rebellious’ or ‘mixed race’. Swedish authorities believed they were creating a society that would be the envy of the world.
Racial hygiene was a big thing, especially in Germany but also all over the, western, world. But even before the nazis and the holocaust, there were plenty of scientists who opposed it, not for moral reasons but for scientific ones. The data werent there, in fact the data indicated exactly the opposite. People just started with an assumption(we are superior) and then tried to find data that confirmed that.
You had cool things like phrenology
https://en.wikipedia.org/wiki/Phrenology
Which said that each “race” had different skulls. Except this was a very easily falsifiable hypothesis because you know, we had skulls and we could measure them. Yet despite that, it was a prominent theory, popular even among scientists.
Change take decades or even centuries. People who went to school in the 1920s and 1930s(when those theories were popular) were very prominent figures in societies in the 1950s and 1960s. Thats why young people and education are so important, they shape the future and define reality.