No, there’s a specific reason the wizard needs human voices, and that’s not it. I’m fleshing out motivations, not doing a rewrite.
This one seems to offer possibilities. Christopher is dying of the same thing that George is going to doom Rosemary with. Perhaps someone has done this to Christopher in order to save someone else. There’s a long line of lives destroyed by the wizard’s plot. When the children complete their quest to save Rosemary, perhaps they’ll find themselves with the means to save Christopher as well, but not the kill-someone-else easy way George is taking. George is faced at the end with the fact that he could have saved his son himself without harming Rosemary, but lacked the strength of character shown by Andy and Hannah.
You’d have to decide whether George knows what exactly is happening to Christopher, and that the wizard he’s working with was involved. Were George’s original dealings with magic what led to someone taking his son’s essence?
How 'bout progeria, the so-called ageing disease.
No thanks. George isn’t abusive, and I’ve read the book anyway. If Peter Jackson has taught me anything, it’s not to watch movie adaptations of books I love; they merely annoy me.
How about simple castration, in an accident perhaps ?