Plants are very efficient when it comes to supplying for people. Plants not only allow us to breath, but we can also feed off them. We can always grow plants. Planting is also better for the environment. Less people will pay for fruits and vegetables. Even with all the advantages of just supplying plants as human food, it would be almost, if not impossible to feed the entire population all year off salads.
The reason is because of the theory "the path of least resistance." The bird is not touching anything else, so it doesn't become our fried birdie dinner.
