I think eugenics, so long as it's non-violent, and the decision for people to form groups out of genetic preference is perfectly fine.
However, Hitler did impose violently on others to make, "living space" for the aryans and fantasized about a war that would "exterminate" Jews so he was acting immoral according to present standards.
Very true, the Nazis were very evil and reckless. It should be said though that they did not 'invent' the idea and even practice of eugenics in modern times, it hails far back. They just made it more effective and indeed imposed it in their sinister way for their dark purposes on others.
Here's a good documentary by independent journalist and researcher James Corbett, it deals with "Big Oil" actually but the euthanasia/eugenics movement that was financed by these families in the UK/US realm is also discussed in the first minutes of the video:
The Nazis 'perfected' this practice later on to the detriment of multitudes of Jewish, Communist, other ethnic people and of course also the mentally ill and disabled people.