I used to love eating meat, till I had to actually think about ethics beyond "whatever the bible says is right" and recognize that all sentient beings are morally relevant
Do you mean sapient? Because plants are also sentient; all sentience is is the ability to react to senses. Sapience on the other hand is the ability to have higher thought, like tool use, teaching, recognizing yourself in a mirror, etc... Finally there is the ability to feel pain which I do not think has a word. Plants from what we can tell cannot process pain, but can process negative stimuli.
No, to the best of my knowledge plants aren't sentient. By sentient I mean "the ability to experience feelings and sensations", which I think is the primary way that word is used. Something could be sentient with no way to react to senses (a paralyzed person for example), or able to "react" to "senses" without experiencing anything (a computer, chemical reaction, or to the best of my knowledge, plants would be examples of this)
the main reason I don't think sapient (as you describe it) is a good marker for who/what is morally relevant is that we can likely agree there are pretty obvious cases where sentient, but not sapient, beings are morally relevant. The first example is baby humans, next is adult humans who are not sapient (terrible injury, disability, etc, could lead to a loss or lack of sapience while retaining sentience), and then even for nonhumans I think we can agree that kicking a dog is a morally relevant action (there could be circumstances where it's justifiable or even good, e.g. kicking them out of the way of a car. But kicking them for fun is wrong)
Sentience may not necessarily mean moral relevance.
For example to be a member of a moral community, which are groups of people who agree to uphold and undertake certain actions with a shared belief of what is good or bad, requires more than just sentience.
For me personally the ability to hold someone accountable for their actions in some way is an important component of moral community membership.
Animals are not held accountable in the same fashion as humans and so it could be argued they don’t deserve membership in our moral community.
If that’s the case then they have some kind of diminished moral standing.
You may then argue that a fetus or comatose person also has diminished moral standing so what obligation do we have in those instances?
One answer to that would be to hold the belief that although a fetus or comatose person is unable to have complete membership to a moral community they are impeded by other circumstances and if those impediments were removed they would be full members. A cow on the other hand will always retain the cognition of a cow, excluding it from full membership.
it's a really useful thought experiment, and once you understand it I think it becomes clear why it matters every time any being suffers or experiences injustice and/or exploitation
Yes it’s an interesting thought experiment and I am guessing you believe it is relevant because you could imagine yourself as an animal and it would be a poor world if you were treated the same way as animals used for food are?
My argument against it would be that the veil of ignorance focuses on members in the society and this isn’t extended to animals.
Yes, if I were in the original position and there was a chance I could be born into a life of being treated like property with no autonomy and completely incapable of improving my lot in life, that would be unacceptable.
From the original position it doesn't matter how you interact with a society, if the society affects you it is relevant and worth considering from the original position. For a human-to-human example, a slaveowner could use that logic to say that slaves aren't members of society so therefore the original position doesn't extend to them. But it does extend to them, they are affected by the society even if they don't get to make decisions about how it operates or interact with it freely, the society's norms, values, and what it accepts heavily influences their life and experience of the world, and so they are very much worth considering from the original position. From the original position, there's a chance you could be the one born under the heel of societies boot, and that society might not view you as part of their society and use that to justify your abuse and exploitation. All the more if you're not human and can't advocate and fight strategically for your own freedom the way humans can
Edit: obviously a human slave, once freed, would be able to participate in society in a way that a nonhuman animal couldn't, but even then there are humans with severe brain damage or severe mental illness who would not be able to participate in society much. From the original position they matter too, even if they can't participate in society or be held responsible for things
according to some, but kant never went in for it. the strongest attempt to marry them seems to be from korsgaard, but howe treated her argument pretty roughly in "why kant animals have rights" (2019)