I think one of the more important lessons from that era is that normal, otherwise decent people supported a monsterous ideology. I think one should at least entertain the possibility that if they were born at that time and place they could have become a Nazi. Awful thought, but it keeps the ol BS meter better calibrated than "not me, I'm not evil."
It wouldn't be that surprising if a number of elderly people that were young during/within the Third Reich suddenly start acting like nazis...again.
A lot of dementia patients basically lose most of their memories past their childhood/early adulthood, so German Granny suddenly thinks it's 1938 again, when the proper thing to say after a toast is...?