You say that with such authority and conviction, but I don't think you really understand the problem well enough to make such a definitive judgement.
Consider the following things;
- Junk food, which is designed and targeted directly at children, and to be addictive, simultaneously using large amounts of fat and sugar
- An environment that's saturated with food, engineered solely to provide nothing other than 100% pleasure but 0% actual useful nutrition
- A transformation of the high street, which has seen 1000% increase in the number of fast food and takeaway outlets, with no controls in place
- Levels of sugary drinks which are targeted at children, resulting in them getting the diseases of alcoholics (type-2 diabetes and fatty liver disease) due to excess, unregulated energy intake.
- Food which is hyper palatable, and energy dense - which offers practically zero satiety, resulting in the ability to drastically exceed normal levels of energy intake
In the final analysis, if you perform an experiment - where you take healthy, responsible individuals and you drop them into an environment that contains a western diet, over time most of them become overweight or obese. (this happened wit Native Americans in the US, when they went from their reservations into the cities)
Not because they suddenly lose all sense of personal responsibility, or because they suddenly become lazy, but quite simply because in an environment such as ours - most people can't hold out against the onslaught of a highly toxic environment, which is why between 60-70% of the UK population are overweight or obese, and 28% of children are obese.
Consider that the obesity epidemic has only been around since the 1980s, we're still biologically the same people we were back then - there's no real evidence for a change in our biology that's driving obesity, but what did change in the 1980s was the onslaught of the food industry and the processed food revolution, that is what's driving the root cause of obesity - it's more of an environmental exposure, than a failure of personal responsibility.
If you don't believe me, go to your local petrol station and just look around at what's for sale, it's totally unrecognisable from a petrol station from 15-20 years ago, the way you're herded through a maze of junk food, sweets and junk - then offered 2 for 1 deals at the tills, is it any wonder the health of the nation is where it is?