Actually, we're not.
Look into the mirror and smile, your front teeth are meant to rip and tear. The front most are your incisors, just behind them are your canines.
Herbivores don't have canines.
While still in front of the mirror, notice that your eyes are side-by-side giving you stereoscopic vision. This is a 'quick and dirty'
characteristic of predators...prey animals have thier eyes mounted more on the sides, generally allowing them a 270ish degree field of vision.
The most damning fact to this arguement however comes from our bio-chemistry; for a normal, healthy body essential amino acids are required. Although
it is true that you can get all of these from eating a combination of plants at every meal, the quantities are very low and you need to do careful
research to find which plants provide the compounds your body requires.
Meat on the other hand provides massive amounts of amino acids and does so in a single source.
Without the benefit of nutritional researchers and a supermarket, our distant ancestors would not have known or been able to attain the specific
combinations of plants required to sustain them.
Vegan's/vegetarians who just stop eating meat suffer from low energy and generally poor health. The reason is that it takes ALOT of careful research
done over a long period of time to ensure that your body is getting what it requires from limited range of foods being eaten. Even when this work is
painstakingly completed, in most cases supplements are needed.
Man is an omnivore, we eat anything we can.