collapse of the old society

Nah, its off in a lot more ways. Bone density, it exaggerates tall peoples "fat"ness, and short peoples "thin"ness, racial differences, differences between the sexes, so on and so forth.

Its a 200 year old formula that's extremely generic. There are newer ones that are better, like waist to height ratio, hip and height, body comp, etc. Each one of those has some flaws too, but the waist to height is apparently pretty damn accurate. Way more than BMI. But it doesn't work for certain ethnicities, children, or people with medical conditions that would enlarge their waist.