You say: "That is a very controversial statement!"... and you are correct. The following is only my opinion, not medical advise, just the way I see it. You have the right to disagree and that is OK.
I paid for a few diets and my friends for a few more. Some were torture; feeling hungry most of the time. I felt like the entire program was just to sell me more products. Others were great; tought me how to read food labels and how to structure my workouts. These diets however are not the norm unfortunately.
What happens to your body and mind when you go on an unsustainable diet? You power through the 30 days using incredible amounts of willpower. If you finish the program (most can't), you look great, feel exhausted but you rock that dress. This is where it all falls apart. During the diet your body is screaming for nutrition that it is not getting but needs. It will go on a hunt to find it and it usually takes it from your muscles and bones. Not so good right? Your muscle mass is your metabolic engine and it is now around 30% smaller. You go back to your regular eating habits and shockingly you gain back all the weight and some. You might decide to do another round of the miracle diet that worked so well before; you see how this will lead to that cycle of yo-yo dieting.
The diet industry answers a demand for quick fixes. We want overnight success and we want hard work. If it is not hard, we don't think it is worth the money. Most of these diets are restrictive, unhealthy, does not teach you how to continue once it's over, therefore inherently setting you up for failure.
To chose a diet plan, look for something that is more of a lifestyle. A program that is something you adopt for the long haul. The plan could include a kick start phase and a maintenance phase. During the program it should teach you how to chose foods that support your body's needs. These programs are pretty simple, you feel full and satisfied. These programs focus on behavior/habit changes, they encourage you to make better choices rather than starvation. Look for support either from a coach or a group either on line or in person.
Diets are not created equal. Do your research before jumping into anything and paying thousands for a program that will be harmful in the long run.