During WWII, Japanese and Nazi doctors committed heinous experimental medical atrocities. Yet, those performed by the Nazi doctors were deemed “crimes against humanity,” whereas those performed by Japanese doctors were disregarded despite the many similarities. The doctors in both countries who carried out diabolical experiments regarded their victims as sub-human, not worthy of living.
https://ahrp.org/1947-nuremberg-doctors-trial-1948-japan-enacts-eugenic-protection-law/
US policy prior to WWII also deemed many with genetic anomalies as not fit to reproduce, subhuman, animalistic and those people were forced to be sterilized, they were studied and very much dehumanized. I think from all I've read the ideas, at least for the Germans, may very well have been learned here in the US as there was much back and forth in the centers for higher education where such darwinistic theories were pushed and eugenics was already being taught. As an aside, the US was also trafficking children from East coast cities, west to work on farms, on "orphan" trains. While some may have ended up in decent loving homes, many were essentially slave labor. These heinous ideas and practices have long been accepted in the US.