At the bottom, we want tasty, satisfying meals. If that means a nice chunk of BBQed mastodon, so be it! The leaf eaters can ruminate in their lotus position until they've extracted all the nutrition from their roots & greens, the world changers are going to toss the bones to the dogs and race off to the next adventure!
The goal shouldn't be to max out the world population with everybody eating beans & rice. Let's raise the bar a little. Life is about change. You live, then you die, no matter what you do. Humans are inventive animals. They created wine, port, whisky, wrote 10,000 cookbooks and have tried every critter under the sun with gravy or soy sauce at one time or another. To paraphrase Socrates, the unexplored diet is not worth living!
Perhaps when all countries provide free birth control, support abortion on demand, educate all their children, not just the boys, provide clean water and basic medical and dental care to their people, then you can go after food producers. The problem is at basis too many people not what they choose to eat.