I don't think anyone would say that genetics is the sole reason behind every obese person's weight problems. Nor that it should form a permanent excuse. But if we are going to discuss the obesity epidemic then it's a valid discussion.
I've had to fight tooth and nail for every kilo I've lost. I've had to cut out all the foods I love, sweat it at the gym, be super disciplined. To get 200g losses and even plateau for weeks. Meanwhile Dh's family who are all rakes, gorge on a diet of junk food, alcohol and their exercise consists of a walk to the fridge. They have amazing genes. I would seriously gain 2+kg a week on their diet. Yet they are size 6/8.
I liken it to two people at uni doing a medical degree. One has exceptional intellect, has been top of their class every single year. The other has only average intellect. The latter states the former has the genetic advantage and they have to work 10 times harder to pass. I doubt people would roll their eyes and suggest that was just an excuse. Yes they may well finish the degree and come out a doctor. But it was far, far harder for them than the Poindexter.