How do you know that plants don't feel pain?

Currently there is no evidence to suggest that plants experience pain as they have no central nervous systems.

Even if we do entertain the idea that plants might experience pain, this would not be reason enough to eat animals that we know are capable of experiencing pain and have the capacity to suffer. If you also consider that feeding livestock uses an enormous amount of plant material which could be better used to feed humans directly, then using this argument to prove that we should eat meat makes no sense as a greater number of plants must be killed.