Body needs a certain amount of carbs.
I think it is about 50-55% and so the best carbs are the ones with the lowest glycaemic index like brown rice and wholewheat bread.
The lower the glycaemic index then the slower the body releases the sugar(glucose) into the body and so preventing blood sugar spikes.
You can get carbs from green vegetables.
Practically speaking, the majority of the wheat and rice available on the market globally is refined to the point where you're basically injecting glucose into your body. You'd think "whole grains" are better for you, but if you do a proper glycaemic test consistently, you'll notice that it's a constant run-up of sugar in your blood. Yes, 'brown rice' and 'wholewheat bread' have a lower response on your blood sugar, but they're still very high.
When your body has that much sugar (50-50% of your intake being carbs), it will not tap into your fat for energy. While this is OK for very physically active people who need a rapidly deployable energy source, it's not for the vast majority of us today. Even among those who do work in the fields, this is excessive glucose. As you age, your natural glucose levels go up, so the utility of this carb intake goes down. From all the people who need that much glucose, I can't think of many besides athletes.
This isn't to say "carbs are bad." The issue, again, is glucose. You can still get carbs from other sources, especially fibrous carbs with lots of micronutrients (things like broccoli, cabbage, etc.) These are the actual "good carbs" that should make 50-55% of your dietary intake, but with healthy proteins and fats making up the rest.
Skyrocketing of various cancers and Heart Disease.
You are trading Diabetes for those.
That's more to do with processed meats than the protein itself. Again, like the glucose problem from wheat and rice, a high % of our diet comprises stuff with chemicals, fortifiers, etc. It's like injecting the world's pollution plus artificially-added vitamins into your body; of course, it's going to cause problems.
However, when you isolate organic and properly raised protein sources (e.g., wild-caught fish, grass-fed beef, etc), you find that they're fine. In fact, the University of Alberta specifically recommended that cancer patients consume animal-based protein. Again, the caveat is that the protein sourcing has to be clean. The moment you put it through today's industrial machine, you'll have problems.
This will give malnutrition problems to a whole generation of growing kids.
And as it is, many people can barely afford food, sugary or wheat/corn stuff is all the energy they can get.
The issue is replacing the glucose-based stuff with green veggies, clean proteins, and clean fats. This is a system-wide issue.