Since both animals and plants feel pain, why are Krishna devotees vegetarian?
If Srila Prabhupada said that anything is conscious if it feels pain, and even trees feel pain, why do devotees prefer vegetarianism since both animals and plants feel pain and have Krishna in them—apart from the fact that prasadam offered to Krishna is sattvic (in the mode of goodness)?
Every living entity is food for another.
"Those who are devoid of hands are prey for those who have hands; those devoid of legs are prey for the four-legged. The weak are the subsistence of the strong, and the general rule holds that one living being is food for another. ( Srimad-Bhagavatam 1:13:47)
Every living entity has to live, so we take our quota while causing the least amount of harm to any living being. Also Krishna says in the Bhagavad-gita that He will accept a leaf, a fruit, a flower, and water when offered to Him with love. He gives no indication that He wants dead animals.
Also in the tenth canto of the Srimad-Bhagavatam there are many references to His drinking milk and eating milk products such as ghee and panir.
Another point is that we are not actually vegetarians. We are "prasad-ivores"—we only eat what can be offered to Krishna—so we eat what He likes. If things are done for Krishna's pleasure there is no karma.
Another consideration: many—even most—fruits are picked from the tree but the tree remains alive. Grains and vegetables produce their edible portion—the seed or flower—and then die of natural causes later on. So it's not necessary to kill them to take the vegetable. The plant will keep producing until it runs its life cycle. Grains come from the plant after it has died a natural death; so with a vegetarian diet there is much less cruelty even considering the welfare of the fruits and veggies.
I hope this is helpful.