Here's a good reason: it's a sin against evolution. Like predators, humans have evolved canines and forward-facing eyes. And while I'm aware that there is animal abuse in slaughterhouses and the like... well, animal cruelty isn't in the McHandbook. What prey... sorry, what [i]vegans[/i] are seeing on YouTube is a couple dickheads beating up a cow for shits and giggles, not standard procedure. Which is regrettable, but the animals still have to be killed. The way these animals have evolved, they would have no hope of survival outside the fence. Chickens in particular; we'd lose all those tasty fückers in less than a decade. Aside from that, meat is fücking delicious and impossible to substitute, vegetables weren't meant to be a main dish, and frankly, the vegans I've experienced are unlikable pricks.