Little Witch, I agree with you whole heartedly, eating sensibly is the ONLY way to maintain weight control AND stay healthy. However the definition of "eating sensibly" seems to be the point even the experts dispute.
About all we really know if that caloric restriction causes weight loss. In dispute is how best to lose this and lose more fat than muscle. High protein/low carb has been demonstrated to do this better in a number of studies.
However when it comes to blood pressure, heart disease, etc., there isn't any agreement yet, nor do I expect there to be since everyone has to support "their" programs and opnions. Remember ego gets in the way of everything, plus the food companies and the drug companies have tons of money on line depending on what "the answer" is.
Some say eating fat is bad, some say eating fat is good and necessary. Some say eat high protein, others say high protein is hard on your kidneys. You get the idea. There isn't a consensus, just a lot of opinions with a few facts sprinkled here and there and twisted to support whatever view the "expert" has.
I suspect that if we step back 150 years, we see a diet that has fewer processed foods, more protein and less sugar, artificial colors, etc. Thus I suspect anyone eating a more "natural" diet is probably going to have fewer problems healthwise.
We can also look to other cultures and find different ways of staying healthy. Another really big point is that exercise makes all the difference in the world regardless of what diet you eat.
We can also agree that some foods have no positive value (save emotional) in the human diet. Sodas, potato chips and donuts are among these, yet are also wildly popular.
As to Atkins, even they recommend a vitamin supplement, and in some cases a fiber supplement in the beginning stages, but again, once you get closer to the maintenance program, you are including high fiber/low glycemic grains, fruits and veges so there really isn't any reason not to get all the nutrition you need from diet alone.
Also keep in mind that few Americans are getting a well-balanced diet and all their nutritional needs met by their diet, but this isn't a question of what "program" they are on, but rather what choices they make in what they eat.
Lot's of diets promote weight loss, but as others have attested to, if you revert to your original habits, those that made you fat in the first place, you will regain the weight.
Permanent weight loss requires permanent changes. However I think the best bet is to choose an "eating style" that you can live with permanently after you've managed to shed the extra lbs.