And beef production, in your opinion, is driven primarily by the consumption needs of the third world urban poor? How much beef does the "overpopulation" eat, relative to the wealthy but slim population of their neocolonial masters? Do those who eat most of the beef need the beef to survive, or do they want the beef for wealth marking and gustatory appeal?
Dude, it was an example.
From the same source, a pound of many common veggies (e.g. wheat, potatoes, lettuce), takes about 25 gallons of water. So of course we could cram more people onto the planet (for a while), by saying that our protein sources MUST from now on be vegetable protein sources such as beans. Well in general beans are somewhere in between veggies and animal protein in terms of gallons needed per pound. So let's say (I believe conservatively), that typical beans require 200 gallons of water / pound. Once again, we can (and have), done the math. A person needs X amount of protein per year. The least water intensive proteins need Y gallons of water per pound, multiply that by N billion people, and you can see how much water is needed - just to get the protein we need.
It's really just math. Observable, calculate-able math.