You're implying that meat has a monopoly on nutrition or it's important. Not true; it's a myth of modern/commercial society. It's also not true that meat contains 'everything we need"(no C, calcium) And once u cook it, it's really deficient.
Many animals are just plant-eaters(horses, turtles, deer). Some of our closest relatives eat just fruit and veg). In nature, meat is survival food, when real-food is scarce. Over time, some animals had to adapt to it.
I've been vegan 18 years. No probs.