Hitler did NOT systematically kill millions of Jews. At most 250K died in labor camps maybe half of which were not even Jews. And they died due to starvation caused by the allies bombing supply lines. The fact that some Jews served in the Wehermacht is very telling that things were not as people are led to believe now. Hitler did have some agreements with Jews prior to the war and at the beginning of it (Transfer agreement). It was a complex situation.

The biggest problem for Jews who discover that Judaism is a disease is that they can't easily find a way out! If they throw away Judaism and their Jewish identity they will have nothing left! And they won't find any Jobs to do. Especially historically as they held skills that only Jews employed. Their food is related to their religion, their clothing, their habits and way of thinking. It wasn't easy for the few odd balls to break out of.

WW2 was supported by Jewish rabbis because many Jews were actually assimilating and throwing away Judaism for real thus the Rabbi felt it necessary to take them back into the Jewish barn so to speak.