Healthy diets are fun, particularly when people stare at your plate in wonder and shake their heads. After telling my friends that I was on a diet, I went to the smorgasbord and loaded my plate once with roast beef (piled high) then went back for roast pork then went back for chicken and turkey before starting on vegetables and fruit. My friends couldn't believe that I stayed so slim on that diet!
I've moved on to another nutritional plan
That was the Atkins diet. More recent research has showed that you lose weight on 2000 calories at breakfast, and gain weight if you have the same food in the evening. More research narrowed it down to the carbohydrates, which are handled better by your body in the morning, and less and less well until 3pm, after which the carbs that you eat are converted to fat in your body, and you should concentrate on protein and saturated fats which aren't fattening.
This isn't the place to discuss the Atkins diet (it will take many pages to do that) but I'll just say that it isn't one diet - it is three or four diets. So when a competitor tells you that you couldn't eat no carbs for the rest of your life according to the Atkins diet, they are talking about the first diet, which should last for only two days to kick-start the diet. Remember a competitor will tell you any lie that is convenient. This is an information site, not a sales site, so I'll eventually have the true story somewhere on my site.
What's wrong with other diets?
My guess is that there is nothing wrong with most diets - they wouldn't last long if there was - and when you get down to it, many of them are saying the same thing in different words. For instance, to eat healthy with the BARF (Biologically Appropriate Raw Food) you should have as much as much of your food raw as possible. Don't eat raw meat because of parasites.
Several decades ago Pottenger did a famous experiment with two groups of cats. One group got only cooked foods while the other got only raw foods. If you are interested in a healthy diet for yourself or your family you might find the results very interesting indeed. Cats getting cooked meals became quarrelsome and there was a lot of bullying. As time went by each generation was less fertile, and there were more deformed births until that group died out. Those getting raw food remained healthy. Look at today's human population. Have you heard about road rage and bullying? Have you heard about increasing infertility? Have you heard about deformed births?
I haven't studied them but I think you will find that the Mediterranean and South Beach diets are also good, designed for long-term use. Even Jenny Craig's diets probably couldn't have remained popular for so long if there was something wrong with them.
Then there are the short-term diets, like the soup diet or the grape diet. These can be great to lose some weight over a short time, but they aren't long-term healthy diets, and would soon ruin your health if you had enough willpower to keep using them. Use them to kick-start your diet if you want a healthy weight.