[ It was rather unfortunate that in hers, most of the men were not so pleasing to the eyes of most. And after what he pulled, that went doubly so for one white-haired Witcher of whom she wishes never to see again. ]

That's right, though it's a lot more involved than just that. Magic is about harnessing Chaos and Chaos is primordial and destructive and dangerous. If it ends up in the hands of the unwary, it will destroy them, starting with their mind. One needs balance and control.