Supposedly there's not enough land on earth for every human to eat meat every day like Americans. Sorta makes the UN's population control thing make sense. However, I'd argue it's a matter of technology. Of course, current trends are towards producing less meat with more land for various reasons, so IDK There's a reason many Indians are vegetarian. They never would have achieved the population density without that. Price is an indicator of scarcity so if demand for meat goes up the price will go up. The fisheries are where we're really screwed, though. Humans cannot continue to take as much as we are, collectively. The fish will disappear, as tuna is already.