The success of dieting programs is that people change their habits from unhealthy behaviors to healthy behaviors. The most successful ones are done in groups that offer emotional support in addition to health education.
The point of these methodologies is to help replace unhealthy development behaviors with healthier ones and to use groups that offer reinforcement of the healthy behavior as part of the process.
Of course, much like diets, not everyone is really going to "buy in" to the new "healthy" habits. They will drag their heels, whine, and generally continue their unhealthy behavior.
A big part of the lack of success of most diets is that the diets themselves change your emotional state. Not to mention that most actually encourage less healthy eating habits.
The American Heart Association for years recommended a low fat diet for heart health, when the studies they were using to justify this decision showed a higher overall mortality for people on low fat diets; they just died of fewer heart-related problems. (If I'm remembering correctly, there were a LOT more suicides in the low-fat group.)
The people who say "just eat less and exercise more!" are also completely full of it. It simply doesn't always work -- handled wrong it can lead to really bad emotional states brought on by the lack of food. Like the above example, you could end up with a lot more suicides, which are pretty bad for your health, no matter how you slice it. Presumably most people who make this claim are not fat or have never tried it, but it's frustrating to see it repeated over and over by people who exercise less than and eat more than a lot of "fat" people.
On the other hand, maybe the metaphor does work: We're recommending or enforcing practices when we really have no clue as to their efficacy. We don't always know what is healthy and what is unhealthy; we have guesses, but then we latch onto them like religion.
The point of these methodologies is to help replace unhealthy development behaviors with healthier ones and to use groups that offer reinforcement of the healthy behavior as part of the process.
Of course, much like diets, not everyone is really going to "buy in" to the new "healthy" habits. They will drag their heels, whine, and generally continue their unhealthy behavior.