Internet, video games, and the rise of cable TV in every home?
I'm not agreeing with the OP. I think he is pretty much totally wrong. But, the internet, video games, and cable TV are mostly ubiquitous in the developed world, while the obesity epidemic isn't. This sort of points to it not being an actual problem. Its like the video games and gun violence debate, which completely ignores the fact that the US isn't the world.
I'm guessing it is a more complex and deeper problem, but our stupid love of sugar is probably to blame. Not just HFCS, which may or not be bad (haven't seen anything conclusive either way), but the fact that it is almost impossible to buy food that isn't overly sweet or sweetened anymore. As a person without a sweet tooth, this makes shopping hell.
Further the quality of our food has declined. When was the last time you had a good tomato; one that isn't pasty, sweet, bland, and completely lacking in acidity? Or sweet corn? It was never sugar sweet, but now it is. They used to be my favorite produce, but now I can't eat them. Hell, buying meat is a PitA now, since all of our birds have gotten flabby, while all of our pork has so little fat that it is almost impossible to cook. Unless your willing to pay out the ass, our food sucks.
Well, I also have friends who eat a meal a day at fast food restaurants, and very few of my friends in my age group (early to mid-30s) can actually cook. Not cooking (i.e. being aware of ingredients), and eating shit, are probably our number one cause of obesity. That and we all sit in offices, on our asses, all day. Hell, I try to eat well, and exercise, and the only reason I'm not obese is because my metabolism is better than most. And even so, I went from 6'4" and 160-70 pounds, to 200 once I hit 30, which is a bit high.