A study shows that fat people who diet themselves thin and stay that way exist in a permanent state of physical and psychological starvation. Would YOU want to live like that? Well, neither do I. If you are genetically predisposed to be thin, it doesn't make you a better person than I am.
Do you think the day will come when we decide that being dark-skinned is morally superior, so everyone goes out and scorches themselves to a leathery crisp in the sunlight? And that those who are genetically predisposed to have dark skin will call pale-skinned people "weak-willed" for not wanting to fry themselves? After all, melanin has some protective qualities, so we all need to become as dark as possible, right? Yeah, right.