Seems the OP is just confused about omnivorous activity.
OP, have you ever seen a comparison of a human jaw with any other omnivores jaw, I assume not.
Here are some examples:
Carnivores - eat meat - have a specialized pair of large slicing teeth (PM4/M1) called "carnassials" that form the major slicing pair of teeth in the jaws, have reduced their other molars so they slice & swallow, with minimal chewing of food.
Wolf
Cougar
Dog
Herbivores - eat plants - have flattened, nearly identical pre-molars & molars. These teeth have exposed enamel & dentine ridges on their surfaces to grind plants.
Horse
Deer
Rabbit
Omnivores - eat meat & plants - Pre-molars & molars have small cusps for grinding, but are not otherwise highly specialized. Canines may be short or long & may be used for function unrelated to killing prey.
Bear
Pig
Primate...which was our evolutionary ancestor?
Human, please take note of the similarities to the other omnivores.
Evolution doesn't lie and there's no indication that humans ever evolved to a state where they only ate plants. Primates are omnivores and if you buy into that whole evolution thing we seem to have evolved from primates. I don't really think there's much scientific backing for evolution though...
If you want proof that humans are omnivores then you need look no further than your mouth. If we were meant to only eat plants our molars would be far more highly specialized like herbivores teeth. Our muscles in our jaw would also have developed differently to encourage our lower jaw to move side-to-side rather than up and down.
Humans our truly omnivores, there is no doubt. We need to eat a wide variety of food in order to be at maximum health. It's not about meat is right or vegetables are right. They're both right, everything in moderation.
I would suggest you read (I'll probably catch flak for this) "The Omnivore's Dilemma" and "In Defense of Food" by Michael Pollan. Although these are more about what has happened to the food industry in the 20th century it gives significant insight into why we need to obtain our nutrients from a wide variety of whole foods, meat, fruits, veggies.