Everyone picks a diet. If you just randomly eat anything thats available to you, in the developed world, you are most likely significantly overweight and at very high risk of diabetes. With rare exceptions, most fad diets will leave you better off than with no guidance whatsoever. Sometimes pointing someone in the wrong direction is better than them walking off a cliff.

Diet science is definitely progressing and getting better. We knew the basics, like what happened when you didn't get enough vitamin C, but the rest of the details are finally getting fleshed out and accepted by mainstream science.

That said, people following the ketogenic diet need to be doing it correctly and under a doctor's supervision. If you half ass it you can end up just eating a shitload of bad fats and miss nutrients while not actually being in ketosis. That will not lead to a good outcome.