There is little disagreement on Hitler being an insane sadist. But unlike the soldiers in the Einsatszgruppen who enlisted the help of copious amounts of schnapps + vodka to cope with the organized massacres ordered by Hitler, and the officers of the Einsatzgruppen, developed psychological issues (different ones).
Arthur Nebbe, commander of the Einsatzgruppe B in Belorussia, committed suicide for not wanting to cooperate with the mass murders.
Karl Jäger, who had declared the Baltic States “Judenfrei” (free of Jews), had to be treated for depression.
All the while Hitler sat in Berchtesgaden ogling a blond chick., keeping his distance from the actual massacres that he ordered.
And not withdrawing the order to exterminate all Jews in Europe (not just displacing them, but killing them).
The lesson one can learn from this, is:
People, even the most wicked ones are inherently good, the problem with homo sapiens, is that they’re all to easily corrupted by homo politicus. As Stanley Milgram https://ludwigvanel.wordpress.com/2017/07/18/2-stans/ had demonstrated, people can’t handle power, including power exerted over them; because they have the unfortunate tendency to obey, fall in line.
Which makes the solution so delightfully simple: remove the institution that corrupts all people, whether leader or follower.