Killing things in order to survive is something that pretty much everything (except for things that get all their energy from the sun) does in nature. Also, plants don't like being eaten either so only sticking to them doesn't really make you any better. Countless plant species have been observed showing defense mechanisms and reacting to being eaten. Some will respond to being eaten by an insect by releasing a chemical into the air that attracts larger, carnivorous insects in order to save it. But because their reactions aren't immediately obvious to humans (they can't run, they don't make loud squealing sounds and they don't have cute little faces) no one gives a shit about eating them.