doctormcgee, I challenge you to find one essential nutrient that is in meat and is not in other products.
B12 doesn't count! B12 comes from bacteria!
Vitamin D doesn't count! We get vitamin D by the sun!
Essential amino acids like arginine, histidine, isoleucine, leucine, lysine, methionin, phenylalanin, threonine, tryptophan and valine all come from plants and bacteria originally.
Cows are big, strong and fairly healthy, if not very bright. They eat grass.
Think of simple trophic levels when considering why raising animals is worse than raising plants. How much plants would a person have to eat before obtaining their fill vs. how much plants a cow would have to eat to have their fill and how much the person would have to eat of the cow to have their fill.
Only about 20% of energy goes from trophic level to trophic level. So by reducing the number of cultured trophic levels, ie. plants -> people, from plants -> cows -> people. We're reducing the amount of environmental energy used up.
It's very, very simple. I really don't know how people can argue with vegetarianism as a principle!