Interesting discussion by Prof Luke Russell (University of Sydney) on the nature of evil:
If someone is an honest person, honesty is part of his or her character. He or she can be relied upon to be honest when it counts. Someone who tells the truth on some occasions might nonetheless be a characteristically dishonest person.
Similarly, not everyone who performs an evil action counts as an evil person. In judging that Hitler was not only an evildoer but an evil person, we assume that evil was part of his character. That’s is not to say we assume he was innately evil, nor that he had no choice but to do evil. Rather, it is to say he came to be strongly disposed to choose to perform evil actions.
Were Hitler, Stalin or Pol Pot innately evil or did they merely commit evil acts? And how do we define an evil act, when violence is an integral part of human/animal nature? What forms of violence are acceptable or unacceptable? Is violence only acceptable in self-defense, in defense of others, or to negate a perceived future threat? Careful study of the factors that motivated Hitler, Stalin and Pol Pot will help us to better understand and protect against future despots. Demonizing despots prevents us from understanding them, leaving us prone to repeat the mistakes of the past.
Read more at Does evil exist and, if so, are some people just plain evil?.