The healthiest populations use a diet that has a lot of its protein sourced from plants. That doesn’t mean we should forego meat completely, because there is some nutrition that we cannot get from plants and need some measure of animal protein.
I agree with your comment entirely concerning the healthiest populations and the fact that one can’t forego meat completely. I would add that the changes to diet for just about every culture have changed radically, not just a little bit but a lot. Historically, people never ate processed foods at the level that people now do. Also, for many cultures (not all), the invention of refrigeration has meant eating meat at a rate that is far higher than their ancestors ever imagined. Ditto for the advent of the entire transportation industry and the changes it has meant to diet. Lastly, most folks just simply don’t get near the exercise or burn off calories at the rate of years ago. What we are looking at is a grand experiment on all of humanity....