1. Plants don't have a central nervous system. They're not sentient and don't feel pain.
2. The fact that something "applies to all animals" doesn't somehow make an action morally justifiable. You're suggesting inaction because perfection can't be achieved.
In our understanding you need nervous system and brain. That doesn't conclude that plants don't feel pain. Pain is how we know about our injury or whatever. That doesn't mean plants will feel that way too. We excrete through our butthole but plants excrete through different way or process. They may feel pain in the way we don't understand yet. Like we now know they are sensitive to light, food, host etc. They emit electrical signals when their body parts are cut. The answer will always be maybe yes or no. We don't even know properly about ourselves, forgot plants and animals.
1. Plants don't have a central nervous system. They're not sentient and don't feel pain.
2. The fact that something "applies to all animals" doesn't somehow make an action morally justifiable. You're suggesting inaction because perfection can't be achieved.