It was popular during a period when folks used science to make policy. It was also popular as a thought experiment on how to improve humanity and society as a whole but when faced with the reality that eugenics required the survivors to ignore the screams of the oppressed, ethics won out.
Same with a lot of really cool progressive folk in the 1900s. Suffragettes, feminists, etc. It was really in vogue until the Nazis.
It was popular during a period when folks used science to make policy. It was also popular as a thought experiment on how to improve humanity and society as a whole but when faced with the reality that eugenics required the survivors to ignore the screams of the oppressed, ethics won out.