Went to Dachau with the family yesterday. Third time I've visited but had a guide this time. I shouldn't be surprised that a people could do such things. After all, it still goes on around the world today. It could happen anywhere under the right conditions--economic despair, someone who comes along and makes you feel special as a nation, someone who feeds your insecurity about all the foreigners around, a need to bring order to society and squelch rampant liberalism.
Then a communist burns down parliament. There's a declaration of martial law. Camps are set up to remove the lawless from the flow of society, to re-educate those who can be re-educated and put the rest to work. The sadists who are always present in society gravitate to such camps. Doctors do experiments on criminal guinea pigs for the benefit of the troops.
No modern society is so evolved that it could not happen again anywhere.