Villains: human nature in its purest form

People say that, when you're writing villains or antagonists, you have to consider that they're not pure evil or pure sociopathy but that they're people, and they should be written as such.

Only today did I realize that I've never had to consider that. To me, villains are people. They are people in their purest form. That is, I don't have to think about "humanizing" them, because, at least according to my worldview, people are inherently inclined towards villainy and malice and selfishness and evil. It's like writing a description of a room and having someone tell you, "Remember, the place you're writing about is indoors." Yes, I might neglect to mention, in a description of a room, that it's indoors, but I know it's indoors, and anyone who reads it is going to get the impression that it's indoors. They might not consciously think of it and I might not consciously think of it, but it's one of those things that is so obvious to me that it's silly for me to imagine that I'd have to remember it.

I guess some people have to remember it because they think human nature is good, or at least neutral. Or if that's not their specific belief, then at least their belief is not something that leads them to believe that humans are naturally inclined towards awfulness in a way that would make a villain nothing more than an example of human nature in its purest form.

What I'm saying is that, today, I realized that I think human nature makes for a perfect villain, and because of that, every instance of antagonist-creating I've been responsible for was done with the implication that, yes, this person is human. That's what makes him a villain in the first place.