We can't evolve? Back then the people who made us who we are so to speak didn't have a whole lot of choice, their bodies adapted to the environment and available food sources. I'd say it'd be going against nature to force people to be any one thing, if someone is happy/healthy with a certain diet lifestyle choice as long as it doesn't hurt others then there's nothing wrong with it. By hurting others I don't mean offending their sensibilities either.
BTW: was vegan for several years but lapsed into bad unhealthy food choices and became convinced my body started craving meat again (reality was just probably craving nutrition plain & simple it didn't care what form, just nutrition). If I had not gotten lazy and stuck with it I would still be a vegan today and still healthy…probably healthier than I am now.