I don’t think that Hitler believed what he was doing was evil. He may have believed about Jews what most Palestinians believe about Jews, even as they get elected to office in America, that they were the sons of pigs and monkeys, as per Koran.
This is an ancient belief, that is older than Islam or Christianity even.
It is comforting to think that most of the evil of this world is committed by people out of pure malevolence. Hitler never smoked nor drank. He had personal integrity in his life. He was able to convince a nation of the evil of the Jew, or maybe the nation encouraged him to believe as they did. Certainly the crowd fed off of him, and he played to the crowd,
Pious believers kill in the name of a cause, an ideology, all the time believing that they are going to make the world a better place. Hitler was merely the Pol Pot of his day. Get rid of the vermin who are oppressing the victim group of the day, be that the proletariat, or the blond lion of Europe, and the world will be a better place.
Psychopaths kill for kicks, and it is very easy to dismiss the world’s worse monsters off as psychopaths,
But it is more accurate to see them as self righteous looking to find the people responsible for the suffering that envelopes them.