My villains have aspects of real people embedded in their personalities. Why? Because using traits from real people make the villains more believable.
Let's look at my more famous or infamous villain - Midnight. She first evolved from a person I know online, one who is evil and would not ever do the things Midnight did. This young lady was extremely secretive, as a young single woman needs to be online, but she remained behind a wall of silence for over a period of years. My wild imagination took that bit of realism and asked myself, "What if ..." The result was Midnight.
Antagonists need "human" qualities that make them rounded, multi-dimensional characters, not stereotyped, flat entities. So I developed a background for Midnight that would make her, if not lovable, at least more understandable.
Midnight took her pain and made others "pay," but many people do that in a less drastic manner. She could be charming and attractive; that's how she could snare men in her web. Often the difference between a hero and a serial killer is how they use their talents and abilities.
So, we need to have "real" villains, no matter how evil they may be.