Sharp's book After the Light, begins with a scene in which a wino urinates on her office door. It was at Harborview that Sharp discovered her knack for saying just the right thing at the right time to people in crisis. Now I had empathy. I knew what people were feeling. She also saw demons.
Dark material exists.
Look at our world. I have come across people who were more than evil. It is opportunistic. That's the key. Evil can't function without opportunity.