I had mixed feelings on that chapter.
First, "obesity is a disease" (since it's been mentioned above) doesn't hit home for me. If you've read my other posts on the other topics related to it, you know by now what I think of 'the natural tendency to put on weight easily': it's a curse in our society, BUT 500 years ago we would have thanked the Lord, the Goddess or whoever our deity was that we were healthy and more able to survive starvation periods. I don't see how a biological mechanism designed to allow us to survive ever deserves to be considered as a disease, no matter how hard things are for us currently. (Of course, that doesn't mean I don't give a fig about gaining weight--if it was the case, I wouldn't be here!
--but I also don't want to view my body as something fundamentally flawed.) What I *would* consider the disease is the current state of our food surroundings. That's a whole other problem in an of itself, I guess.
Second. Regarding the psychological aspect. Yes, non-obese people may engage in the same behaviours, but maybe not to such an extent. And fast metabolism or not, there comes a point when you will gain weight all the same if you overeat by a lot. I know we most often tend to use the term 'emotional eating', because to be honest, it does have a clear meaning. But maybe a more appropriate word would be 'behavioural eating' (cf. also what SusanB wrote: "What if that symptom (overeating) was combined with sluggish genetics and a food centered cultural upbringing"). We've been given tools to learn to eat in certain circumstances, for instance, so is it so surprising that we go on applying them once we're adults, and then of course it starts to really weigh on us (yes, pun intended)? Ever growing portion sizes and huge plates are probably part of this, too. The importance of our environment is overbearing, I think. This indeed probably plays a role.
Now, can we say there's no emotional component? Maybe the emotional component is here, but not exactly in the shape of food itself, and food is just a part of it. I don't know exactly how to put it. I'm not even sure I've formed a clear opinion on that matter yet. But to me, obesity is not biological only. There is a clear behavioural component to it. Whether it is only a matter of semantics or not, it is here IMHO.