Dan, I have an update:
Several people have e-mailed me to tell me—very politely—that I'm an idiot. Rowling's world is full of gray characters, they argue persuasively, including Aunt Petunia (she took Harry in, didn't she?), Mundungus Fletcher (Dumbledore trusted this petty criminal, who makes off with everything that's not nailed down at the Order of the Phoenix clubhouse), and Cornelius Fudge (the former Minister of Magic isn't clearly on the side of evil, but he sure isn't helping). And they point out correctly that the Wizarding version of Gollum is Peter Pettigrew.
I still think Rowling is less interested in exploring moral complexity than some of her fellow fantasy writers, such as T.H. White, Ursula K. Le Guin, and Philip Pullman. But maybe she'll surprise me.