I just read something appalling, but it sounds true to me, the same way that Primal sounds true to me, because it's supported by scientific facts.
Here's the money quote (page 125-126, paperback version).
"We're asking the wrong question. It's for the right reasons: we want a just world where every last child is fed. But our species overshot a long time ago and *it can't be done.* In the end, phantom carrying capacity can produce only ghosts, and they will be hungry ones. We're using up fossil acres, harvesting sunlight that's been stored away for thousands of years. Once it's gone, there won't be any more. "Facts are not repealed by refusal to face them," writes Catton. We - human race we - are going to have to face the facts if we have any hope of easing our way toward true sustainability while valuing human rights and preserving civic order. The alternative is a grim and ugly scenario of mass starvation, plagues, racial and tribal strife, misogyny, fundamentalism, and accelerating ecosystem collapse."
I strongly recommend this book. You will be shocked. (And it will give you some strong comebacks to people who say "but eating meat isn't sustainable!")