"Given the heinous crimes they were about to commit, there is a tendency to think that the members of the Einsatzgruppen were all bloodthirsty sadists. It’s a comfortable way of thinking about the history, but it’s wrong. Whatever else motivated these killers, it wasn’t mass psychopathy. Two of the four commanders of the Einsatzgruppen, Arthur Nebe, head of the Criminal Police, and Walter Stahlecker, who had led security forces in Norway, volunteered for the job.9 The others were appointed, including the intellectual Otto Ohlendorf of the SD. He wasn’t the only cerebral commander within the ranks of the killing squads. In Einsatzgruppe A, eleven of the seventeen most senior leaders were lawyers; nine held academic doctorates."

The point is, people can be psychologically motivated to commit unspeakable atrocities. The entire book is about how the National Socialists achieved that. Thus:

"Alfred Metzner, a driver for one of the Nazi commanders [in Poland], remembered that “pregnant women were shot in the belly for fun and then thrown into the pits… . And Walter Mattner, an officer charged with organizing a ghetto clearance, recounted his actions to his wife in October 1941: “I aimed calmly and shot with confidence at the women, children and numerous babies… The babies flew in great arcs and we shot them to pieces in the air before they fell into the ditch and the water … Oh, Devil take it! I’d never seen so much blood, filth, flesh. Now I understand the expression ‘blood-drunk’.”

Many such cases.

— Rod Dreher on The Nazi Mind: Twelve Warnings From History, by Laurence Rees,