Evil is not villainy. Keep this in mind. The word "villain" comes from the Old French vilein and the Latin villanus, referring to a serf or peasant who worked the land of a villa to which they were bound. It literally means an indentured servant; I believe there's every likelihood that our modern conception of the term as an evil-doer came from an attempt to cast these servants and peasants as though they were the antagonists of a noble class with inherent power and privilege over them.
So, villains aren't evil. They're indentured servants who do what they must. What, then, is evil?
I believe evil is maliciousness. Cruelty. Evil is pathetic. To be evil is to be snide, conniving, genuinely mean for no reason other than to be mean. No one is evil for a good reason, they're evil because they want to be evil. Evil is mockable. Evil is laughable. Evil is the strangest behavior a person could express in this world.
There's a reason villains in stories are the popular characters. We empathize with them, relate to them. If their causes are good enough, we believe in them. Any character can be a villain. Someone is either the hero of their story or the villain of someone else's; it's a matter of perspective, not morality. That's the role a villain plays: the antagonist of someone else's story, often one who believes they are the hero of theirs.
Evil people don't believe they're the hero of anything. They know they're rotten, and they're ashamed of it, but they enjoy being cruel too much to ever stop. Evil people are no one's villain to anyons except themselves. A common phrase when referring to the truly evil is, "the cruelty is the point".
Yes. The cruelty is the point. But it's a point of weakness, not a point of anything else. It shows that these evil people are like poorly-supported children, which in all honesty is an insult to children, because children can usually manage themselves far better than an evil person can.
Yes, evil people are weak; they are weak to themselves, to their need to see others in worse positions than they are, because it makes them feel like they've done something that day. In truth, all they've done is show their weakness, their lack of strength, their snivelling hides that run when faced with the truth.
So many people think their own vulnerability is weakness, but their vulnerability is the strength. They have faced evil and felt their feelings no matter what. Vulnerability is the means by which one can avoid evil nd cruelty, and it's the one behavior an evil person would never do simply because to be vulnerable is to believe you no longer need to be weak to your petty mindset and that you're capable of rising above it — that you might even want to rise above it.
For an evil person, they'll never get that far.
The cruelty is the point.
And villainy must never be confused with being truly evil.
That's what evil is.
That's all it is, in the end.