> Your ruminations about how they problem can or cannot be solved are not relevant to what is causing the problem.

It is, you just don't want to admit it. People didn't all individually decide to change their lifestyle, their lifestyle changed due to their environmental conditions changing. People aren't fully rational actors, but they are responsive actors.

People respond to their environment, or their circumstances, or whatever else by making decisions. We both know this is true, but it is not possible to reconcile this reality with the position you’re taking here. Unless you want to start taking people’s ability to choose away from them, by say setting up obesity internment camps, then any solution you could possibly imagine must require people to individually start making different decisions. Your insistence on absolving people of this responsibility certainly isn’t constructive.

> People respond to their environment, or their circumstances, or whatever else by making decisions.

And their decisions vary based on their environment and circumstances. Alter the environment, and you can easily get better decisions and results.

One thing some people do when trying to adopt a healthier diet is to change where they keep healthy vs unhealthy food in their house, to make healthier food more convenient and unhealthy food less convenient. They alter their environment to encourage better moment-to-moment decisions. We can choose as a society to do the same thing.

The point is not to make unhealthy decisions literally impossible; it's virtually always possible to make unhealthy or healthy choices, but how easy or hard they are can vary quite a bit. The point is to make healthier decisions the easy, default option.

> One thing some people do when trying to adopt a healthier diet is to change where they keep healthy vs unhealthy food in their house, to make healthier food more convenient and unhealthy food less convenient. They alter their environment to encourage better moment-to-moment decisions. We can choose as a society to do the same thing.

Putting aside the "healthy vs unhealthy" food contrivance, how do you propose that society decides to keep healthier food options in individual people's houses? If somebody chooses to do that, they are individually choosing to make a lifestyle change. According to you this strategy is a "smooth road to failure".

> Putting aside the "healthy vs unhealthy" food contrivance

It's not a strict binary system, but there's definitely foods that are broadly healthier or unhealthier. Unless you think Dorito's and broccoli are equally healthy.

> how do you propose that society decides to keep healthier food options in individual people's houses?

I would focus on the things the government can control. Transportation is a big one: the government already controls roads and streets, and the US has pushed car dominance in transportation options for decades now, and it's been very successful, with most trips done by car.

Switching to a model where walking, biking, and public transit are co-equal with driving overall, would result in more exercise in transportation, among the other benefits of multimodal transportation.

Tons of people actually do like walking, biking, and public transit when those options are actually good -- you see a lot of Americans comment on this when they visit other countries that do better here -- but in most US cities, they kinda suck. There's usually little that's useful within walking distance, biking feels both unpleasant and unsafe, and buses/trains are slow and unreliable, if they even exist at all.

Those are all fixable issues, it's just a matter of where we choose to invest as a society. We've mostly been investing into car-dominant transportation, and so cars usually make the most sense in our built environments. And we're talking about societal-level choices here; people don't get to individually choose if the buses are reliable, or if bike paths are unsafe, or if zoning allows for neighborhood bakeries and grocery stores.