No, it's not! Pain is an entirely human concept. Just because plants do not suffer in comparable ways like humans and animals doesn't justify that killing them is acceptable. In fact, plants clearly react to environmental stress. Some plants are also able to warn other plants of the same species when hurt by herbivores so they can release chemical deterrents.

From my point of view the statement "what does not suffer can be killed" is morally much less defensible than the statement "to live I sometimes have to kill".

ya.ya.yo!