He based his refusal on religious grounds, arguing that since God sent him this disease, it would be impious of him to resist it.
This is a great question. God may send you a disease and overcome it to be better. When I got sick, I finally saw the disabled community and have been an outspoken supporter. I have counseled others, not given little fortune cookie bits of wisdom. Maybe God sent you a disease to change your life and give it more meaning. Michael J Fox has raised over $1 billion dollars for Parkinson's research even more money than he earned for his roles in Back to The Future.