Agreed. Correct portions, less calories, healthier foods, and adequate exercise all contribute to fitter people, and all of those factors require willpower to make good decisions.
The soda mention also brought to mind those individuals who think they can guzzle "diet" soda or eat other "diet" foods and lose weight. If the regular product a junk food company sells is bad for you, chances are the diet product is bad for you too, just in different, more hidden ways. Not only are people not trustworthy enough to limit themselves to 1 diet serving, but the artificial chemical crap that goes into some (but not all) diet foods is horrible for your body.
People are better off just eating healthier, not substituting with the "diet" version of junk food.