In Dungeons and Dragons – well, in 3.5 at least – morality is divided into two axes. A person can be Lawful, Neutral, or Chaotic. At the same time, a person can be Good, Neutral, or Evil.
When it comes to how the law axis interacts with evil, I like to put it like this.
A Lawful Evil person will break into your house and take your stuff because someone told him to do it. Or because he has persuaded himself that he has some sort of right to to it (typically that you owe him some sort of debt).
A Neutral Evil person will break into your house and take your stuff because he wants what’s in it. Vey simple, very straightforward.
Chaotic Evil is different. I’ll separate them into two kinds.
Firstly, a chaotic evil person will break into your house and take your stuff to prove to you that society is bullshit. That locks are a lie, that your comfy, safe little world is an illusion. That is: they are sending a message. They have a political goal. At bottom, they fear the fact that normal people trust each other and can cooperate. They themselves are incapable of it, but they see how people are strong in groups, and they don’t understand how it’s possible to live like that. Therefore, they attack that trust, that “social capital” where they can. To remake the world into something they understand.
Secondly, and less philosophically, a chaotic evil person will break into your house not to take your stuff, but to vandalise it. For the sheer joy of destruction. They will fuck shit up not to achieve anything, but because fucking shit up is what they like to do. It’s an end in itself.
And yes, there really are such people. Criminal pricks. Quite a lot of them, actually. It’s not a fantasy, it’s not even much of an oversimplification. I’ve seen them, I’ve met them. They live around us. We as a society do what we can to minimise the damage they cause.
Don’t try to understand ’em. Don’t try to make excuses for them, or account for what they do. There is no deeper layer to their behaviour, there is no “there” there. Why do bullies bully? Because it feels good. The fact that this is what feels good for them is what is evil about them; and the fact they can’t or won’t restrain their impulses is what being chaotic is. “Why”, after a point, ceases to matter in that it doesn’t change the is what it is.
They are just crims, that’s all.