It seems to me that this is essentially a question about the definition of evil. Is it a matter of intent or a matter of result? Is it some defect in brain chemistry, is it learned, is it some sort of taint of the soul (if one believes in that)? Likely, what makes someone evil is some sort of combination of these things.
I recall hearing about research into this from Columbia University and, if I recall the results correctly, overwhelmingly people who commit heinous crimes have three major things in common: sociopathy and/or other disorders, childhood abuse, and brain injury.
This makes sense to me. We look at the people who commit these terrible crimes, and even if they show some predisposition to that sort of behavior, they all have tragic childhoods as well. Hell, even if the likes of Bundy or Dahmer abused animals or attacked their peers as kids, I’m sure we all probably knew someone like that growing up, who probably wasn’t sexually or physically abused or suffered traumatic brain injury, and more or less learned to cope with society as adults.
So, really, what is evil? If a person simply lacks a moral compass, for whatever reason, is it fair to call them evil when they truly can’t see the difference? What about a person who knows that something is wrong, but just doesn’t care, is selfish, believes they can get away with it, or somehow justifies it? If a person commits one or a few truly heinous crimes are they more or less evil than someone who commits more but relatively less heinous crimes? If someone is born with a very serious disorder but otherwise treated well and turns out to do heinous crimes, is he inherently evil? What if someone is horribly mistreated and “made” into a person who does those things?
At least to me, evil is just such a loaded word, carrying religious and social and historical and all sorts of baggage, that it’s really impossible to get any sort of useful meaning out of it. Though I think most of us would consider someone like Bundy to be evil under almost any definition of the word, I feel it’s as much tragic as anything, whether it’s because he truly couldn’t see the difference or because he was made that way through abuse, neither of those possibilities is a conscious choice that a reasonable person can or would make.
So it seems to me that, labeling people who commit heinous acts is the greatest evil, if anything is, because it’s a way of separating us and treating those people as less than human. That is, it’s the “normal” people making a conscious choice and by separating them, many of us can easily justify to ourselves that they’re just the broken outlier, and we can feel comfortable with shoving them in a tiny cell for the rest of their lives or executing them.
Instead, I think it makes the most sense to just label certain acts as evil, based upon just how far outside the rules of morality those acts are. And though we very well may need to protect ourselves from people who commit evil acts, through imprisonment or execution or whatever, it just doesn’t make much sense to me to label the person himself as evil.