It is possible to eat vegetarian diets that contain all necessary vitamins, amino acids, minerals, and protein to support human growth - although this may require more care than a normal diet. Animals are not necessary to manure fields now that we rely on inorganic fertilsers and, with accelerating greenhouse problems, it is unlikely we need more methane. However, animals are very good at turning poor quality vegetation, in inaccessible and infertile areas, into high quality meat.
