Let’s think about this in two ways. First, do plants actually feel pain in any way similar to an animal or human? Most honest people would agree that there is a huge difference between cutting a leaf from a tree and killing a dog. In fact, a human’s experience of suffering is closer to the animal’s experience of suffering than the animal’s experience of suffering is to any potential “suffering” in plants.
This common sense experience is backed by scientific evidence, too. We know for a fact that plants lack brains, a Central Nervous System, and anything else that neuroscientists know to cause sentience. Some studies show plants to have input/output reactions to certain stimulation, but no study suggests plants have sentience or any ability to feel emotions or pain as we understand it. We can clearly understand the difference between a blade of grass and a pig.
Non-sentient biological life reacts to stimuli, but does not have subjective experiences or a conscious will of its own, and can not be harmed in the same way as sentient life.Charles Horn, Meat Logic
Second, let’s say we discovered that plants actually have something akin to what we understand as “sentience”. In this case, the crucial difference is that we need to eat plants to survive, but we don’t have to eat animals. Furthermore, more plants are used for meat production than for vegetable production because the animals we eat are fed plants, and they can eat way more than us. So if we truly care about plants, it is better to minimise plant usage by feeding humans directly with them, rather than feeding many more plants to animals to then eat ourselves.