Any "diet" is just that - something unsustainable for most people. Keto is not unhealthy in my opinion as well as based on the current research out there, however I use it as a part of periodization. You can eat a very low carb diet and not be keto, which is what I plan to periodize with. I am planning one day a month of higher carbs to keep hormones in check and condition my body to know how to run off fat while still being able to handle carbs. When I am in the condition I want, I can slowly ramp up carbs until I'm at a modest amount. People do not need more carbs than a keto diet provides, it is just easier to sustain a more lenient very low or low carb diet. What a keto diet does do is teach you how to eat. Weight Watchers or anything that takes the accountability out of making food choices is going to result in rebound weight gain because they do not teach you about nutrition. Like I said before though, people need to do what works for them. Maybe keto is is not healthy in your opinion, but for me, when I am limiting carbs I am at my healthiest, so it's what I do. Low fat diets have been loosely linked to progressive diseases of the brain, like Alzheimer's. Again, what is "healthy" for you may be "unhealthy" for me. I'd love some quality evidence supporting the health detriments from eating low carb.