There is the evil act, the evil person, the evil society. The evil person has a habit of evil action. Short of collapse of his place in society, he finds no means of breaking his habit and seeing his friends as he once did. And the evil society is one that operates with a principle of gaining strength by harming individuals. From the isolated act, through the person's habit of action, to the mutually rewarded and punished habits of a society there is progressively less freedom to change for the individual.
When we say a person is evil, it feels like we are saying something much more serious than saying he has done something evil. It means the opposite of what one might expect: this is not someone who's made a self conscious choice to do bad, but someone with a habit gained by practice that leaves him each time it's practiced with less freedom not to do bad in the future. The evil society too, is not the one most ill willed, but the one that has the least of free will.
When our friend appears evil, it is frightening to think that she has less choice now to remember how you once were together. You would feel better if you believed it was just a bad choice, now she will come back to you when you remind her of what was so good in your life together.
When a society is evil, it asks you to do many times and shows others doing many times evil actions. Trains move millions to concentration camps, gangs of police shoot hundreds of people at at time. The numbers make it too clear that something bad is happening. You naturally realize your own individual vulnerability. The numbers have to be reinterpreted so as to refer back to you in a supporting way. The more of them moved away, the more killed, the better for you. You deliberately change how you see.
I imagine saying to my wife: you think it is not wrong for a woman like you to trick money from men, they deserve to be tricked, and you deserve the rewards of successful trickery? That the number of successful tricks is so high proves that the world is arranged well. As the friend from a world outside of trickery, I have no place in your life any more.
My wife in fact said to me: "I have all my different needs now taken care of, I was a fool to settle for you, I don't have to now". I feel the world spinning around me. I say to myself, she's become evil. I am afraid of her. She is not the person I used to know. She doesn't seem to know me at all.