Plants are not sentient, they can't be sentient on a biological level (cells are too slow to transfer information, plants don't have a central nervous system). Whereas most animals are sentient. But even if plants were sentient, and you care about not harming sentient life, it would harm the least sentient life if you consume a vegan diet, since it takes 130 kg of crops to produce one kg of meat, so eating plants directly would spare the most plants.
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