Hitler's executioners are a good example how law abiding citizens with weak , consciences, accepted state induced violence and became mass killers. To understand the reaction or lack of reaction of the Germans, we have to understand the gradualism of poisoning the Germans with violence. The Final Solution started with the boycott of Jewish stores, then came the beatings, Kristallnacht, expulsions, concentration camps , Einsatzgruppen, all culminating with the gas chambers. It was a slow, irreversible process. Antidotes to poison are developed by graduate increasing the amount of poison.
Violence is induced in a similar manner.
The main purpose was the degrading of the victims in the eyes of the killer, to make his job easier. It was Primo Levy that formulated this idea. Cruelty is very contagious. To understand the mechanics of the Holocaust, we have to recognize the overbearing power that a Totalitarian state has over his citizens. Stalin starved, shot or froze to death about 20 millions Russians.