“I don’t get it: Why would people who worship Satan be against witchcraft?”
The Muslims in Indonesia and Malaysia all believe in this stuff. There are several reports a year in Hong Kong of Muslim maids trying to cast black-magic spells on their employers by doing things like putting small amounts of urine or menstrual blood into coffee or tea which is supposed to magically bring bad luck(A good argument for a non-Muslim Filipino maid BTW).
When I was an undergraduate I had a roommate in the dorm who was from Jordan. The guy was a devout Muslim but he carried charms and wards against evil spirits wherever he went. Maybe he was an exception but at least in the Islamic countries I have had any experience with such superstitions and a believe in demons, ghost, malevolent spirits and things like that is quite common. In Asia it is almost like the Muslims still believe in all the Hindu/Buddhist deities but can’t put a god-box outside their door like the Buddhist to placate them.
Mohammed supposedly went out into the desert and preached to and converted jinns and spirits that lived there to Islam. It is one of the miracles in the Haddith.
The frightening thing is that it is WE who are are the odd ones out :)