If Everyone went Vegan...

About Peta's amusing, yet sometimes true "wrong answers" in this "pie graph"...

1. Obviously. That's the whole point. 
2. There are at least some obscure nutrients one can only find in animal products (and no, protein is obviously not one of them). People who can't find artificial sources for said nutrients could likely starve to death, or at least be deficient in said obscure nutrients. In particular, there is vitamin B12, the deficiency in which may be why PETA is generally so insane. I do not know why we need said nutrients, but I believe they became useful either from an extinct fruit source or our ancestor's habits of eating insects. 
3. "And cow shall inherit the Earth" is a humorous idea, but most domesticated cattle don't have that many tools. They'd need to tag-team with other bovines to pull this off and send us into the Age of Bovines. 
4. We're not at risk for a Biollante situation. Hell, we can't even make a friendly plant person like Cosmo.
5. Oh boy, the terrorists haven't even fucking started... They also want to nix zoos and wildlife welfare, and even pets.