I don't have a theology of demons, but I can say that I've experienced the presence of really scarey & oppressive energies while working with the seriously mentally ill, drug addicts, and severely abused children. When I consider Berg's utterances while under the influence of some "godly" spirit promising to rape and kill, I wonder what could be more discernably evil and NOT godly?
I've also experienced the presence of powerful healing & loving energies while working with very sick people. My father died last Thursday. I was blessed to be with him as he drew his final breaths and passed over. As he let go, I felt the spirit of Sojourner Truth moving and speaking through me: "But this is an old body, and will soon get out of this world into another, and wants to say when he gets there, Lord, I have done my duty, I have told the whole truth...I'm going home now like a shooting star."
Was Sojourner Truth standing there in the room with us? I don't know--I don't have a well-defined theology of angels and spirit helpers, either. It's simply that my own experience leads me to believe there is more to life than meets the eye.