>>23122798
In the 1920s to 1930s genetics was in its absolute infancy. Physicians were in the forefront of the eugenics-project and part of it were gigantic question marks about how genetic diseases are inherited and which diseases were genetic in the first place.
Besides condoms, abstinence and sterilization there was no contraception and the population of the mentally ill, the mentally disabled and physically disabled would've exploded (that was the fear), because they had a higher birth rate and the state/the healthy society has to care for them.
It was about curbing a population explosion of ill people before it becomes impossible to stop the spread.

There is immense cruelty but also immense compassion for future generations in that ideology.