All true. But when I use public transportation the social contract extends to those who played no part in their circumstances. I have no problem with a guy that has schizophrenia because that was the hand he was dealt. When a family of 4 takes 6 seats and the surrounding area for cheeseburgers, well, I didn't sign up for that.
Hypothyroidism, the medical condition many people claim to have, affects 4.6% of the American population 12 & up (http://www.niddk.nih.gov/health-information/health-topics/endocrine/hypothyroidism/Pages/fact-sheet.aspx) but the obesity rate is close to 70% of adults. Even being extremely generous and doubling the thyroid cases plus an extra 5% for miscellany diet issues, we're under 15%. What of the other 50%+? I'm sure many have valid reasons, but not all 50%.
This is one of those issues that I'm very curious about so I observe when I grocery shop. Almost without exception I can see how terribly fat people eat. A lot of it can be laid at the feet of marketing. Low fat, gluten free, natural, all the bullshit that people have bought blindly instead of doing the legwork themselves. So they buy 4 boxes of Kraft mac and cheese that has the new all-natural dye made from paprika instead of the artificial coloring because we've been told natural is good and artificial is bad. But the bullet we run from is never the one that gets us, and the problem was never the dye. They buy Gatorade because it isn't soda and frozen dinners without reading the label because it says Healthy Choice or Lean Cuisine. They avoid whole milk and fat because, despite evidence that those who consume it are trimmer, they've been told it's bad. I don't think it's an exaggeration to say that I don't know that I've ever seen a fat person grocery shopping where I couldn't pinpoint 85% of the problem at a glance.
I disagree with it not being a lack of willpower for many, though. I don't eat dessert. I never eat candy. I don't drink 24 ounce ice cream drinks. Pizza is a treat. If I indulge, I remove the cost from somewhere else in my diet. It isn't that I don't want these. It's that I value having shoulders wider than my waist and a flat stomach and a high-functioning (or even functioning) heart more than I value a donut. Exercise is pay now for a distant reward. Food is reward now for a distant cost, good or bad. Bad is easy. People may value being able to eat everything that gets within range of their Lil' Rascal motorized scooter and that's their prerogative. But people need to own their choices. Look at the market for weight loss pills and supplements and tell me that people own their choices. They want to not give anything up and still have the body they claim to hate. I'm sure they know all this, like you said. The great thing about facts is that they don't change if you don't like them and the push lately seems to be to obscure the harder truths instead of putting your head down and suffering.
Think about the cost to our environment to keep fat people fat (the fat people that live on packaged, processed food, at least). All the shipping, the plants, manufacturing, the commercial farms, the hormones, the antibiotics to prevent disease caused by the poor conditions. The drug-resistant diseases that spring up from these. The new pesticides required to keep the commercial industries going. It isn't that they would go away, but if one family requires the food that fed three families fifty years ago they aren't helping. Now multiply that by hundreds of millions.
TL;DR: The Fats caused drug-resistant gonorrhea because they can't say no to Hamburger Helper.