What about morals, and ecology, and sustainability? If everyone were to eat only animal products (providing people in developing coiuntries could afford it, which they naturally wouldn't by far), we'd need several extra planets and thousands of times extra water. It takes something like 15,000 liters of water to produce one kilogram of beef. It is already a problem that Western people are stuffing themselves with meat, while more than one billion people are starving and lack - exactly - proteins.
See I was wondering about this, if it really held up, though I was thinking in terms of land use.... Anyway they always say you can feed more per acre than you can with livestock. But what about say with free range vs penned up live stock... I don't mean the space the animal takes up but ecologically how bad is it in comparison?
If you just have the animal grazing on field grass and not having anything grown just for the cattle, I think that might actually be better environmentally. For with vegetables you're using fertilizers, herbicides, pesticides, all with runoff problems...then there's the gas used driving around making rounds with the fertilizers, herbicides, and pesticides... There's a lot of work and energy going into it. What gets used on an old cowboy style cattle drive, firewood?
And the land use in that case isn't "used" in the same sense as a garden is, the grazing animal eats a bit of the grass, moves on, in the meantime plenty is still growing and sequestering CO2. Now it's different if you're cutting down forest for the land, but if you're just using pre-existing plains there doesn't seem to be much harm at all.
So anyway, I'm just thinking its not so cut and dry with how much energy, water, land, etc. that meat takes. It really has to depend on the practices involved, and where you're getting it from.