It promotes a kind of magical thinking which spreads and leads people down the path that fruit will cure their cancer.
I think it’s healthier on a personal and societal level if we try and fail instead of quit. Worst case we learn what doesn’t work.
This is coming from someone facing a life-threatening illness. I hear lots of shit advice all the time. I've chosen to separate myself from support groups that circulate dangerous ideas, and I think I'm better off.
The alternative isn't giving up. It's doing what we can with what we actually know based on science-based medicine. That might include seeking a second, third, etc. credible opinion.
Unfortunately, there isn't always an answer. Countless people suffer from conditions that no one understands.