Humans eat meat, the high calories derived from a largely meat diet are what gave rise to our larger brains.
Animals that do not eat meat have no need for a large brain, in fact, its a liability. Human eyes are situated close together and on the front of the face rather than the sides to afford us depth perception, a trait that is only unless for carnivorous animals. An animal that does not need to hunt would be better off with eyes on the sides of the head, allowing a wider field of view.
Human teeth are not large and we don't have claws because humans do not hunt food in the tradional manner of other carnivores. Man is an entirely unique meat eating animal, in that our larger brains have resulted in no need for a strong body, fast speed, strong teeth, slashing claws or even the sense of smell. We hunt by wits alone...everything else proved a liability on energy that was cast off.
There is evidence to suggest that early hominids developed our more complex hands and then bipedalism before our large brains. It is believed that these early forms of ourselves used rocks to smash open the bones of carrion, AFTER all other predators and scavengers had picked it clean. The bone marrow inside would have afforded us enough calories to begin developing an even larger brain, allowing us to push our primative tool making abilities to new levels. At some point we aquired the ability to make fire, and from there our path was chosen. No other animal possesses the ability to harness and control fire, and with it we were quickly able to rise from the precarious position of scavenging prey to the ultimate predator. A predator whose intelligence allows it to adapt immediately to different food sources and threats. Whereas other animals have to adapt through evolution, humans can adapt through innovation.
Early on in hominid evolution there was an offshoot of animals with large morals and powerful jaws that are believed to have existed on a diet of plants. They died out early on in their existence.
Nature is brutal. She does not afford animals abilities that they do not need because they are all energy liabilities. A large brain is a massive liability on resting energy. If a species is to have a large brain, it has to use it to its advantage. Otherwise, its just a waste of calories.
IMO, to deny myself meat is to deny the fact that I'm human. Others will feel differently, saying we've "evolved beyond that". Humans have been the supreme predator on the scene for thousands and thousands of years, there has been no stimulus for us to evolve since that time. The only reason we do not have to eat meat is because we have constructed a society that affords us the choice. It wasn't always an option. If you choose not to eat meat, thats fine. But don't tell me you're a superior being because of it. We're the same animal. And we're all taking some form of life to sustain our own, that is...unless we are plants.