My long-suffering wife and I were talking theology on the walk to the china store on the weekend, kickstarted by OBA's meditation on the difference between "Good vs Evil" and "Enlightenment vs not being enlightened". Apparently Christian theological orthodoxy falls somewhere in the middle of those two: Good exists, but Evil doesn't. Evil is the name for "absence of Good" that's more convenient than that three-word scare-quoted thing.
That's certainly not the way I'd thought it worked.
I still think there's a difference between lack-of-benevolence and malevolence; my wife agrees, but doesn't think it applies to the spiritual realm. She argues that humans have free will, so we can will evil as well as failing to will good, and those are different; angels and devils, on the other hand, don't have free will. They do what they do because they are what they are, more like animals than people. And those things are Good to the extent that they participate in the glorification of God. Even when they're inimical to humans, as the actions of devils presumably are.
Weird, hunh? Angels and devils, more alike to each other -- and to animals -- than to us. I wonder if I believe.