This is an interesting quick take from Business Insider on why good people do bad things, Two jumped out at me: The notion of self-image (labelled under the Galatea effect), which I think is repeated in two other points, is a powerful notion. How do people see themselves such that there isn't a strong resistance to the impulse to do evil? The other is on euphemisms to label an evil thing with a neutral new name (labelled under the Power of Words). While we can appreciate how words are just words, a new label will add a new dimension to an act, which in the case of a deliberately bland or generic euphemism renders it above judgement.
Something else that struck me is (of course) the Christian response. What is the right self-image for anyone to embrace? It is simply that of the image of God. Each human being who accepts this deliberately will never be the same. Far from being defined by one's actions at any moment in time, it is far more correct to view one's entire nature, which does not change and is therefore a firm foundation on which to ground one's decisions. It gives us a clear template, and even a non-believer can appreciate the importance of standards of behavior, hopefully well-considered ones that do not change on whim.
As for the words we attach to acts, there's this time-honored saying: the Truth will set you free. Pretending that an evil was not committed does not make it so. The problem is that it is necessary to look carefully at the two facets of evil: the morality of the act itself and the culpability of the actor. We can't get to the bottom of the act without distinguishing the two. Both are crucially important. You can't do good medicine by pretending that the patient isn't sick. You have to identify the condition after a thorough investigation if there is to be a proper cure. At the end of the day, evil demands a healing response, not condemnation. Because it must be thorough, and because it can be acted out from deliberate reasoning, it is necessary to trace that reasoning and root out why someone chose evil, assuming they did. Ascribing culpability is ultimately about prescribing the cure, because while there's time, amendment requires great deliberation. Conflating the two can result in a disgust with judging what one person did as evil or not, particularly if there's the fear of being condemned irrevocably or "sentenced" unjustly in some way.
A final thought on that article was to find it amusing, considering that we already know about them, particularly the ones I comment on above, but at the same time, it's good to find recent findings in psychology pointing to unchanging truths.