Technically Night soil is not vegetarian.... Bactria, nematodes, microscopic organisms are all consumed by even the most anal Durrian types, as well as by animals which are labeled herbivores. Ruminants actually are bacteria-vors who get their life force from colonies of gut bacteria that break down the plant matter.
The vegan agenda does a terrible job at providing trans-generational evidence that would prove their way of life is sustainable.
Among the more vegetarian-ish tribes that have flourished, they have practices which include, in some way shape or form, the use of small amounts of non vegetarian foods. So the Claim that people could live and thrive from generation to generation on entirely vegetarian diets, cannot be proven.