I think it really depends on how we're defining the diet. As I said, avoiding excess carbohydrates, especially the simpler kind, is probably a good thing. Excess of anything isn't good.
But I would be very careful about a long-term keto diet (beyond 6 months), and I just wouldn't do it without consulting with a physician first and at regular intervals. There might be some versions of the keto diet out there that would be okay, but I think a lot of people really mess around with biology and don't know what they're doing. They read blogs or watch YouTube and don't realize people are pimping diet fads to make money.
Yeah, but a well formulated diet doesn't require anything at all from people hawking products. The only generally recommended supplements are electrolytes - sodium, potassium, magnesium. All you need to do is eat real foods, and avoid starchy carbs, and of course avoid grains (a relatively recent addition to the human diet) and only minimal sugars. That means lots of fat but if you look at our ancestors, they prioritized fatty parts of the animals they killed, as do wild animals. What we eat, the lean meat, was the last thing eaten. Our ancestors of course ate liver, heart, brains, etc.
A lot of keto diets recommend high-fat diets, which are going to cause heart and cardiovascular disease if there's excess fat over the long-term.
There's a growing body of evidence that the real risk to heart and cardiovascular disease are the refined carbs and sugars in the 'western' diet, not the fat.
A high-protein, low-healthy carb diet (i.e., low-fiber) is going to stress your renal system. Strict avoidance of carbohydrates almost certainly means avoidance of fiber, which is going to change your gut microbiome. Doing that weakens your immune system and increases the risk of cancer. I don't really think any of these are good outcomes.
That's not true since you can eat all the salad, broccoli, etc. that you want. You avoid grains with some fiber, but there are plenty of other options.
I just don't think there's any credible medical science to back this up at all. The benefits of grains, fruits, and vegetables are well-documented. It's true you can overdo it with pretty much anything, but you're much better off overdoing it with fiber than fat or protein.
There really are no required carbs. You can survive and thrive on nothing but meat. A number of native people did/do that, and more societies clearly ate meat as their main source of fuel, then veggies and fruit in a very short window of time every year. I'm not arguing that veggies and fruits aren't healthy - they are in moderation. Some people can thrive eating vegan or vegetarian. Bottom line for most of us is if we eat whole, unprocessed food, we're a long way to good health. However, those with T2D or other metabolic problems, essentially anyone seriously overweight, can very likely see all their health markers improve by eating keto or LCHF. Or, alternatively, fasting.
The core problem for almost everyone obese is insulin resistance, that shows up a decade or more before blood sugars go up, and insulin resistance (an excess of insulin, really, all day trying and failing to lower blood glucose) erects barriers to burning fat. That's why people need 6 or 7 'meals' a day - they cannot get to the fat stores for fuel. So they need to do something to lower insulin and keep it there for a large part of every day to allow their body to burn the fat they want to get rid of. Keto does it, as does fasting.