Thanks for your feedback.

Here I would guess that you're underestimating the influence of (evolutionarily conditioned) straightforwardly base motivations: c.f. the Milgram and Stanford Prison Experiments. I recently ran across this fascinating essay by Ron Jones on his experience running an experiment called "The Third Wave" in his high school class. I would guess that the motivation that he describes (of feeling superior to others) played a significantly larger role than abnormally explicit reasoning in the case of the Nazi regime; that (the appearance of?) abnormally explicit reasoning was a result of this underlying motivation rather than the cause.

There may be an issue generalizing from one example here; what your describing sounds to me closer to why a LW poster might have become a Nazi during Nazi times than why a typical person might have become a Nazi during Nazi times. On the other hand, I find it likely that the originators of the underlying ideas ("Aryan" nationalism, communism, Catholic doctrines) used explicit reasoning more often than the typical person does in coming to their conclusions.