Animals like lions and our early ancestors had no choice but to eat meat in order to survive. We live in a modern agricultural society, rather than a hunter-gatherer society, so we have a huge array of plant-based proteins. Unlike animals or our ancestors, we don't need meat to thrive. Also, there's nothing “natural” about factory farming. Our ancestors ate meat a few times per month, not three times a day, nor did they eat products produced with pesticides and antibiotics.