The type of personal integration we attain – or the effective lack thereof – depends on what possibilities our life situation offers us for the development of autonomy. It is a distorted development that is the root cause of the pathological and, ultimately, evil element in human beings.

The struggle for autonomy heightens our aliveness. Insofar as the socialization process blocks autonomy, however, this process engenders the evil it attempts to prevent. If parental love is so distorted that it demands submission and dependence for its self-confirmation, social adjustment turns into a test of obedience and the child’s efforts to comply bring with them the loss of genuine feelings. The human being then becomes the true source of evil.
"The Betrayal of the Self: The Fear of Autonomy in Men and Women"
[..] if one is in touch with one's own unconscious reality, I think one would have to admit that in all of us there is a piece of Eichmann, and if you ask why, on what basis do I say this, then I would ask you whether you have lost your appetite when you read that in India people were starving, or whether you have gone on eating. As soon as you have not lost your appetite, when you knew other people were starving, then your heart has hardened, and in principle, you have done the same which Eichmann did.

I don't think, that if we are really in touch with the inner reality of ourselves, that there is any crime, or perhaps any virtue, which we cannot discover in ourselves. We shut ourselves [off] from the awareness of our inner reality, we project the evil to our opponents and enemies, and believe that the good is in ourselves; individually, nationally, and group-wise in general.

But if you can really see that every one of us, carries all of humanity, the good and the evil, within himself, then indeed is very hard to be a fanatic, then indeed it's very hard to be a judge, then indeed would follow, a deep understanding, if not love, of your fellow man. Which is part of being truly a person.
lecture called "The Automaton Citizen"
All human evil comes from a single cause, man's inability to sit still in a room.
[George Orwell] hardly writes anything about fascism, at all. He hardly writes a single essay saying why you should be against it. He takes it for granted, that when you look down the gun barrel of Hitler and Mussolini and Franco and fascism and nazism, that you don't need to be told what's wrong with it. Here is everything you hate. Here is ever bullying father, every crushed, repressed mother, every sadistic prison warder, every exploiting capitalist, every racist and Jew-baiter, every thug and bully and sadist and exploiter that has ever been all rolled into one, and then refined and double-distilled and then re-done again so you've got the absolutely pure of everything that's hateful. We tend to sneer, or I've heard people sneer, at the use of the word "evil" by politicians. By politicians on should usually suspect the use of this word. But it's not possible, if you want to write morally, or you want to write critically, or you want to write historically, it's not possible to do without this word.
The sad truth is that most evil is done by people who never make up their minds to be good or evil.