I'm not arguing that every (or any) particular diet is perfect for everyone. I'm objecting to your claim that 'if you've tried a couple of diets and failed then you probably can't lose weight'. That's a hell of a strong factual claim, and if it's wrong then it's incredibly unhelpful. So what's the evidence? From what I can make out the case is 1) you believe there's strong evidence that it's nigh-impossible for a few people (mostly yourself?) 2) lots of people try fail 3) lots of different methods are put forward and lots of crap is talked about it.

I imagine that the same points are true for plenty of things that lots of people set out to do but which are difficult: learning a language, becoming a good cook, proficiency at an instrument, stopping procrastinating, getting a well-paying job... The last place I'd expect to see a counsel of despair would be here, tbh.

If there is stronger evidence that I'm missing, I'd be massively interested... and obviously you can ignore all the above!