Semi-articulate midnight musings:
Anne Lamott's excellent book on writing, Bird by Bird, was lying around the house, so I picked it up the other day intending to put it away, but ended up re-reading some bits of it. I liked this:
Only in the comics and formula movies do we get any pleasure from destroying totally evil and sinister villains, because in those cases they've been systematically depersonalized. They commit only acts of atrocity and sociopathology, and they say terribly evil things, and then we get to ritually kill them. There can be, at the end of the [story], the relief that comes with justice.
[But] you can't write down your intellectual understanding of a hero or villain and expect us to be engaged. You probably have got to find these characters within the community of people who live in your heart.
Or, to put it another way, if you want to write really compelling villains, try to empathize with them. Which might not be a bad idea for the villains of real life as well—regardless of which humans you happen to consider villains.
I suppose an eminent philosopher once said something similar: "Love your enemy." (Another eminent philosopher once said "We have met the enemy, and he is us." I leave it as an exercise to the reader to reconcile these remarks.)