I'd have to liken fasting to static stretching prior to working out: It was done for thousands of years, millions of people thought it was good, but in the end, science has proved that it's actually harmful.
Unfortunately, the "it's been done that way for a long time, so it must be good" attitude still prevails, and science is ignored.
Anecdotal stories and denial are one thing, but science can't be argued.
"You do not truly know someone until you fight them."
- Seraph, The Matrix Reloaded