I think pretty much any dietician you ask can pinpoint the cause of society's obesity very simply.
Convenience foods, and liquid calories. We eat too many high calorie, prepackaged foods, and drink too many calorie laden drinks.
My house is an oddity, and most kids stare at me in confusion when they come over and ask for juice. We don't keep juice in the house typically. It's a rare treat for parties and such. We keep some soda in the basement for entertaining, but the kids don't drink it. It's typically milk and water at our home, and coffee for mom.
I just packed my daughter's lunch, and the 'junkiest' thing she got in her lunch was dried cranberries, and she only got those because I'm out of the yogurt I typicaly send. It's usually a sandwich, fruit, yogurt, and a container of water. I'm a boring mom. lol.
But, all the good habits in the world can't end all obesity.