Destroy humanity?  Nah.  But I do think that if the obesity epidemic continues to worsen, they will eventually help to bring about a societal collapse which results in hams experiencing one of the following fates:   Worst case scenario, outright starving to death or dying from dehydration because they can't be mobile enough to find edible food and drinkable water. Slimming down because they can no longer access an abundant flow of cheap food. Dying from not being able to receive the medical care and medications which ordinarily would help to keep them alive.  Obviously if we reach the point where these scenarios are happening, it isn't just fat people who are going to suffer.  Almost everyone to some degree would be having trouble.  But the good news is that being fat won't be possible anymore for the vast majority of people for at least a good long while.