Well i guess its all about how you look at things. While witchcraft is originated from satanism that doesn't make harry potter evil, in order for it to be evil it would have to be able to lead ppl away from God.
Some of the most seemingly innocent things are inherently and wholely evil. Harry Potter absolutely has the power to turn people away from God and does so to children from a very young age. It offers nothing to the kingdom of God but an example of the kingdom of Satan. Even simple distractions like "not-so-evil" tv shows are enough to be considered harmful.
Even Disney movies are crazy bad if you really pay attention to what they teach. Removal of parental authority, if the parents are even there at all, rewarding disobedient children (every Disney movie ever made), and effectively dismantling the structure and hierarchy of the family unit in the mind of the kids watching them.
Harry Potter is really no different. Harmless as it may be to some, to others it could have devastating long-term consequences regarding their belief systems and belief development. Maybe a kid growing up obsessed with Harry Potter gets older and decides real witchcraft isn't much different than the series they loved as a kid and because the dangers were not taught to them by the books and films as a kid, they venture into the real thing, solidifying their false belief system and leading them further and further away.