Ever since Christians started hunt on witches, there was this idea that black magic is somehow bad because it causes harm.
However, I find it difficult to understand such a position. For example, guns cause harm, yet guns are necessary for self defense. Sure, bad people can use guns for bad purposes, but that doesnt mean we should all just get rid of all guns, because thats unrealistic.
Same principle works with black magic. It can be used for self defense, to destroy or control the ones who want to harm you. Plus, many spells in black magic arent meant to cause harm to others. Some are just love spells or money spells powered by offerings to powerful beings. Some are transformation spells. Some are spells to control dreams. I dont really see why would it be considered bad. Like, considering it bad wont make it go away, and there is no actual way to protect from black magic anyway if black magic user has greater powers.