neuralnerd

what creates a duty to NOT HARM something?

About all ethics is about reducing harm. If you don’t know that harming is bad I don’t think we can have a discussion.

you can’t prove plants aren’t sentient.

And you can’t prove something is sentient. But scientists have criteria that help determine whether a species is sentient. See this review for example.

even if you could, why should sentience matter?

I already answered. If something can’t be harmed there no need to prevent harming it.

what ethical system even accounts for sentience as a factor of right behavior?

About all animal welfare:

Respect for animal welfare is often based on the belief that nonhuman animals are sentient and that consideration should be given to their well-being or suffering, especially when they are under the care of humans.[4]

The question was “why is eating meat bad?”, my answer is something like “because to have meat you must harm animals”, and someone answered that “we always harm something when we eat” and my answer is “no, there are foods that you can’t harm because they are not sentient”.

Because if something is not sentient it cannot have negative experiences, so it can’t be harmed.

The term sentience has no concrete meaning, so how can you base your moral judgements on this?

It does have a concrete meaning. Scientific papers usually define what they are studying. For example the Review of the Evidence of Sentience in Cephalopod Molluscs and Decapod Crustaceans has a definition. It also has criteria to evaluate it.

Plenty of plant life has senses and are able to “feel” things.

Having reactions to external stimulus is different from having feelings. Feelings require consciousness, or sentience.

Even having nociceptors doesn’t mean you can experience pain (see the above review in the “Defining sentience” section).

If something (living or not) cannot experience suffering then you can’t harm it, by definition

This follows no definition of harm that I am aware of, and I do not agree with it. If you are not aware that you have been harmed, you are still harmed. So you should also be able to be harmed even when you could not be aware of it. Therefore, I do not accept this sentiocentric (just learned this word) argument.

Yes you can be harmed without knowing it, but it still must have a negative effect on you. If something can’t have negative (or positive) experience then how can you say it’s being harmed?

If I throw a rock to the ground, it doesn’t make sense to say I harmed the rock, because a rock can’t experience being harmed. Being sentient is having this ability to experience being harmed. That’s why I meant it’s by definition that non sentient beings can’t be harmed. The word exists to distinguish what can and cannot experience harm (among other feelings).

There are good reasons to treat different beings differently but they should be based on the beings’ interests, not their species

And this is one of those reasons. A human’s (or any other animal’s) continued existence is mutually exclusive with the food’s continued existence.

But having food doesn’t necessarily mean harming something. And even if it does, different foods have different level of harm. We can choose the foods that minimize harm.

If we do not follow speciest dogma, we might as well eat other humans.

Indeed meat eaters don’t really have good reasons to exclude human meat.

In your example the “bad weather” means “bad for me/us” (a farmer would probably disagree, for example, as would some animals). Indeed morality is about what’s “bad to others” or to everyone. But since OP didn’t specify to whom, I considered it meant “bad in general”, for the one eating and for the others.

OP included “Ethical reason for consuming animals” in the accepted answer, so answering about morality doesn’t seem wrong.

It’s not about “all life” but about “all sentient life”. Only beings that are able have pleasant and unpleasant experience should be considered. If something (living or not) cannot experience suffering then you can’t harm it, by definition.

Sentience is studied scientifically. It cannot be stated with absolute certainty but scientists have good sets of criteria and experiences that helps identify it. With the current knowledge it’s almost certain that all mammals are sentient, like us. Fishes and birds are also very likely to be sentient. Some species of insects are probably sentient while others may not be. And plants are likely not sentient.

But even if all living things are sentient, it doesn’t change very much. Speciesism means treating beings differently only because they belong to some specific species. There are good reasons to treat different beings differently but they should be based on the beings’ interests, not their species (and studying sentience helps identifying these interests). It’s very likely that we do less harm by growing plants than by breeding animals. And even if it was the same amount of suffering we would still do less harm by avoiding eating animals because breeding them to eat them actually requires more plants than just eating plants. We should seek to minimise suffering and avoiding eating animal is a good way to do that.

It is indeed about morality. Morality is about what is “good” and “bad”, so it’s perfectly in line with OP’s question “why is the consumption of meat considered bad”.

Religions have arbitrary morality so it doesn’t seem very interesting to discuss why these religions allow or forbid to eat their specific set of animals, unless you’re studying these religions.

Moral philosophy on the contrary tries to study morality with real arguments. In almost all cases they agree it’s bad to harm others while it’s not necessary. Even with our intuitive morality most people would agree with that. And in most cases eating animals products contributes to harming them and is not necessary. It was not necessarily the case in the past, but today it is. So eating animal products nowadays is immoral.

The environmental problems only adds additional harms on top of that by causing harms to even more animals, including humans.

Because it’s speciesism. If we started giving birth to humans to eat them, that would be absolutely outrageous, but to do that to animals seems perfectly fine to most people. Animals have the same desire as we do not to be killed or abused, and to live a happy life.