But Katherine, any religion which turns people away from the truth has evil in it. That's not to say it is completely evil, but the more it deviates from Christ's Church, the less good it is. And Wicca is in fact very far from the Church.
You may have a point in that the Harry Potter books have many Christian symbols and themes. I have not read them; I don't know. However, the religious effect of these books on people in general, as highlighted by the media, is a growing acceptance towards witchcraft and magic.
As I believe these practices to be condemned by God, and all cases of them either non-existant or result of demonic intervention, I think this growing acceptance is quite an evil thing.