How the fuck can anyone get obesity in the first place seriously, I'm not an American myself so I really don't know about the eating culture there, but anyone with more than double digits IQ knows stuffing themselves with junk food is an indisputably retarded behavior and being obese is no one but your fault.
It is ultimately everyone's responsibility. I've been blessed with a fast metabolism and have never been overweight, but as a dirty American i know many overweight and obese people.
While we all need to be accountable for our own choices, living healthy in the US is a real uphill challenge.
One factor you have to consider is convenience. Its almost impossible to eat healthy in the US unless you have a lot of home cooked meals. Restaurants are all packed with high carb, high salt foods. Fast food, gas stations, corner store... it's all bad here. Its an uphill battle.
I've been to Canada and the UK, the two countries probably most like the US, and from what I've seen its much improved. All sweets in the UK taste like 50% the sugar, which I prefer anyway, but way healthier. Much less salt across the board. Bags of veggies, stir fry meals, ready to go at the gas station at good prices. Meals for one at Tescos people pick up on the way home from work, almost as good as home cooked. We have almost none of that. If you aren't going to the grocery store, 99% chance you're eating bad.
That's a big reason why more than half of US citizens are overweight, and over one in three are obese.