As my Dad used to say when I was growing up "Cows eat plants, people eat cows".
Who knows what imbalances could be created by indiscriminately bypassing the food chain and eating vegetables that haven't been preprocessed by the appropriate herbivore.
You don't see a pack of cows out hunting rabbits for dinner. Imagine what the result could be if we ignore the importance of the food chain. It's there for a reason, I'm just doing my part to keep it intact.