Calling something "evil" is implying an external force (often linked to religion), that I don't think should be used. It reduces the responsibility of the person doing "evil" acts.

I think the missing ingredient is simply not caring about the outcome. It could be because they don't have empathy (sociopaths), or that the society has trained them into normalising obedience to the cause (facsism / communism) or inhumanized their targets (consentration camps).

Acts can certainly be described as "evil", but I don't agree that "evil" is some type of force that affects people.