I think the problems with popular notions of dieting - and this is going to get OT, but my mind's on it at the moment - are intermingled with problems of praise and self-esteem in society. You can see, on almost any occasion, a women's magazine at the grocery store which will say "lose 10 pounds!" next to a picture of a giant chocolate cake slice. Anyone who has successfully dieted knows that it involves lifestyle changes, thought and research into making better decisions, and a gradual build of accomplishments and confidence over months/years, not a quick-fix recipe, and if you succeed, the chocolate cake will essentially leave the dinner table and your mind.
But the mindset of a fragile ego is to want an immediate resolution and insignificant changes to habits - whether it's through badgering others for acceptance("there is no problem with me, right?"), falling for snake-oil pitches, using drugs, buying expensive medical procedures, etc. We don't educate people towards building real self-esteem, so we end up with a massive segment of our population perpetually sitting on the verge of severe emotional distress.
This is especially unfortunate because, at least how I understand it and was raised, self-esteem is cheap to create. It's formed by focusing the dialogue on real accomplishments and immediate consequences and avoiding attribute-based judgments(which have an unbounded magnitude and finality that make them impossible to frame in a positive way). You can find this theme running through books ranging from the classic "Between Parent and Child" (which my parents used), to a variety of books on business and networking, to Cesar Millan's dog training method.
Going back to dieting, the consequence of our corrupted dialogue is a glut of poor advice, guilt trips, and fad-following. Now that I've tried actually "playing" with diet, I've discovered that it can be a lot of fun; you just have to get away from good food/bad food/ideal numbers dogmatism and take a more from-the-ground-up, intuitive approach.