What about killing plants?
It is not wrong to eat plants for the same reason that it is not
wrong to kill bacteria. Every time I brush my teeth, I kill
thousands of bacteria, yet I see nothing wrong with doing
so.
The distinguishing characteristic between animals and bacteria is that animals are conscious beings capable of feeling pain and suffering. Animals are capable of feeling happiness, joy, and sorrow. Animals are capable of feeling a desire to live.
Bacteria, on the other hand, just like plants, and just like rocks, do not possess anything similar to a nervous system, nor do they exhibit any behavior which would indicate that they possess consciousness. Bacteria are not capable of feeling pain or suffering. Bacteria are not capable of feeling a desire to live. Bacteria, just like plants, and just like rocks, are not capable of feeling anything whatsoever.
When you kick a rock, you do not have to worry about whether or not you are inflicting suffering on the rock, or interfering with the rock's desire to live, since rocks are incapable of such feelings. It is for this reason that it is not immoral to kick rocks, and it is for this same reason that it is not immoral to eat plants.
Follow up questions:
How do you know that plants can not feel pain?
What would you do if we hypothetically discovered that plants do indeed feel pain?
Don't plants move their leaves to follow the sun?
Aren't there some religions which believe that plants possess a soul?
What if we killed the animals without inflicting any pain on them?
How do you know that other animals can feel pain?
Where in the animal kingdom does consciousness begin?
Is it ok to kill animals which do not possess consciousness?