>>698921The problem lies in the inefficiency of the food chain. 90% of the nutrients an animal consumes is burned off as heat, leaving 10% for the meat and tissues. The same goes for humans eating meat.
Following this train of thought, if it takes 100 pounds of grain to produce 10 pounds of meat, which produces 1 pound of human, why not just skip the middle man and use only 10 pounds of grain/vegetables for 1 pound of human?
The process, clearly, is more complex than that, but at the most basic level, it's more efficient to grow things for people than for cows (for people).
I'd also like to point out that modern industrial feed is not hay, but primarily corn and similar grains. This corn, generally, has lower quality (because of lower standards), but it's still corn. And in that way, you are still creating the same environmental impacts for feeding cows as feeding people. Producing meat takes more land, which makes more environmental impacts.