Except humans are obligate omnivores. *Some* members can survive in a subsistence mode on vegetable matter, but others cannot and many cannot do so long term in a healthy manner.
Any zoology grad student can point at our tooth layout and explain to you exactly why animals develop that incisor / eyetooth / bicuspid / molar order, and it's not for chewing leaves. It's there because our bodies, by and large, have a dietary requirement - driven by nutritional and physiological requirements - to tear and consume animal proteins. There is simply no getting around it.