If you identify 'progressivism', 'environmentalism', etc., as lineal descendants of ecumenical Protestant Christianity—that is, when you see them as essentially

If you identify 'progressivism', 'environmentalism', etc., as lineal descendants of ecumenical Protestant Christianity—that is, when you see them as essentially religious movements—it is easy to understand the emergence of vegetarianism and especially veganism: they are the exact analogues of religious dietary laws. Hinduism has a prohibition on the consumption of beef and other meats, Judaism has kosher, Islam has halal, and progressivism has vegetarianism/veganism. In all cases, the purpose of dietary laws is the same: they are hard-to-fake demonstrations of piety.