Eugenics was a common belief among the movers and shakers of many regions of the world. This is a very nuanced question and although I think fighting the war to "stop" the Nazis was important it was not a moral decision by goverment. IBM made a fortune off the Holocaust. Henry Ford was an anti semite and eugenisist. In my opinion moat of this stems from the idea that you can perfect humanity and human societies. It always end in tears for large groups if people.