The thing is that the majority of fat people don't have a metabolic defect. They have a lifestyle defect. Sure, one eventually compounds the other, and I'm not saying it's simple. But the entire 'slow metabolism' meme is annoying and generally untrue. It's not, to be honest, easy for anyone to lose weight, but for most people it's doable. Obesity is a huge health threat and not something we should normalise. People have slow metabolisms because they sit down all day, consider exercise a walk across a car park, and portion control to be running out of Pringles.