If you're arguing that weight gain or a sense of willpower are entirely genetic, I think the onus is on you to provide proof.

Introducing the likening of weight loss, something that everybody is capable of, to changing skin colour and changing your gender/sex is absurd.

Eating below your energy expenditure will cause you to lose weight. Every time somebody decides to eat a (or many) burger or a donut, they have the choice not to do that. Genetics aren't forcing anyone.