I agree that people need to eat well and do exercise, but at the same time society needs to be built in a way that makes this easy to do. I live in one of the few walkable places in the US. In some rankings it is considered the fittest place in the US. It is not a coincidence. Yes there are still overweight people here, and fit people in very un-walkable areas. But in terms of population stats better environments lead to healthier people.

At the same time I agree that for the individual they need a mindset that they can change their circumstances. The US won't be made walkable over night if ever. There is unlikely to be a ban on producing or advertising high sugary processed food. But even in such an environment you still have tons of agency over your choices.