The Nazis and the Question of Moral Judgment

Regarding your approach to judging evil deeds and the connection to the Nazis, I have some ambiguity. I will put it this way:
According to you, there is no justification for saying that the Nazis were immoral people. Because in judging a person, one must take into account their own positions. Hence, it is possible that the act is truly immoral (the murder), but since it is possible that the Nazis have a different theory – for example, the Jews want to kill us – then the killing itself is not immoral. At most, there is a mistake of fact here or a lack of motivation to think properly, but that does not really make the person clearly immoral.
My question: I agree with the aforementioned scheme, but it seems that sometimes it is possible – more or less – to identify whether the act was done as a result of an excuse or evil. For example – if the Nazis really believed that the Jews were problematic and so on, then they should have imprisoned the Jews, punished them to a reasonable extent and so on. The very fact that they conducted horrific experiments and horror stories, from this we can understand that it was pure evil.
So why did you conclude that they were not immoral people?