Good post, teetime. I agree that it's a very complex issue.
And I'd add that though I agree with the suggestion that physical activities at schools could (and should) be broadened to suit more personality types (not easy with tight budgets), exercising doesn't actually burn many calories so I find it irritating that it is mentioned so often in relatioon to the obesity epidemic.
I think it's more of a mindset thing that needs to be sorted. I'm not sure how this could be achieved except through the education of attitudes. My father's approach was to stress the importance of a healthy body being necessary for the smooth running of a healthy mind. That worked for my siblings and me but then my dad was quite a character and a bloody good teacher too.
I'm still not sure if there's much the state can do except get, preferably correct, information out there for people to use. In the end, keeping one's weight healthy is each individual's responsibility. Plus, as a species, we need to adapt to there always being a surplus of food available. That luxury is not in our genetic code because until recently in human history, except for the very powerful and rich, it simply hasn't been an option. Yes, I really do think it's an adaptation problem, complicated by modern medicine and surgery that keep us alive where previously we would have died (heart diseases, diabetes, etc).