"I wouldn't even put it down to emotion or genetics -- we've had those for millennia. Western diet (i.e. ignorance toward healthy eating) can easily take most of the blame. "
Nick, I would have to disagree with you. I think a lot of people that are obese have issues with their eating. I mean even with the misinformation about diet in the west, everyone still knows that eating fast food is bad for you, but people still do it. And don't kid yourself into thinking that there aren't skinny people eating what the government tells you to eat, because there are.
To be honest I think a lot of it comes down to addiction to food. I know that I am still struggling with this. I have eaten primal for about a month, and I feel great. I have lost weight and I look much better. I have more energy. Basically it just feels great eating healthy. But, I still crave unhealthy foods on a daily basis. I have set out two designated cheat meals during the week that I still go crazy on. But they keep me sane. Soon enough I will cut them to one cheat meal, and then eventually none. But I still think about eating bad food every day. It is quite the addiction. I think that most people that are very overweight share this addiction. It is unfortunate to say the least.