An old school mate of mine who I've reently been back in touch with, is a proper born again Christian fundamentalist. He did geology at university (pre shiny-eyed conversion), but now believes the earth is 4,000 years old.
BMI's not perfect, but for most people it's a handy guide. If you're 6 foot, weigh 16 stone and your BMI is 35 then if you're NOT a professional rugby player or body builder, you probably could do with losing a bit of weight.