Jane, whilst I appreciate and understand your feelings on the subject, any diet should be about changing your eating habits for the better on a permanent basis. For me (who has been a yo-yo dieter for years), I have finally come to realise that there is no going back to eating 'normally'. My normal eating habits are what makes me gain weight. I know that, in order to continue to lose and then maintain wieght, I need to change my eating habits, which is what I've done. With any diet, if you restrict your food intake (which is basically what any version of a diet does), as soon as you start increasing the amount/calorie count/fat content of your diet again you are bound to put weight on.
A diet, for me, is not an interim solution. I have slowly come to the realisation that if I eat a diet of chips, cakes, crisps, biscuits, chocolate etc. then I am going to gain weight. The basic maths is to ensure your calorie intake doesn't exceed the number of calories you burn in a day. I have been losing weight (on average) at approx 3lbs per week. I know that if I eat more in a particular week, I won't lose as much. If I eat less, I will lose a bit more. Hopefully, by the time I reach my target weight, I will have learned what I need to eat in order to maintain that weight.
I suppose what I'm trying to say is that it doesn't necessarily mean that Slimming World is not a good diet - at the end of the day, it works (admittedly, not for everybody) and that's what counts. But, the important thing to remember, which is probably where a lot of slimming clubs fail, is that you need to permanently change your eating habits. My DH is forever asking when we can go back to eating 'normally' and I have to keep reminding him that this is it! There is no going back (not for me anyway). Having been fat for longer than I remember, when I eventually get to be thin, there is not a hope in hell of me going back to being the lardy blob I was