The relevant distinction is the ability to feel pleasure or pain. If plants can feel pleasure or pain, then, other things being equal, we should not eat them. — Herg
This is different from what you had said here
What makes an action immoral, in the end, is that it adversely affects ... any sentient being. — Herg
I supplied the emphasis here to draw attention to the gist of your original claim, the one I was responding to.
My argument responding to the original claim, which is not addressed in your subsequent post, was that
(1) Not all animals are sentient.
(2) If there are some non-sentient animals, a fortiori, they do not feel pain.
Consequently,
(3) if the claim that it is morally wrong to eat animals is completely grounded on the fact that they feel pain/pleasure, there is no moral reason for people to abstain from eating at least non-sentient animals.
In addition, even assuming your position is really that the morality of eating animals depends on pain/pleasure and assuming further that sentience necessarily entails the capacity for having pain/pleasure (a claim I don't think is true, but whatever), that still does not end the inquiry since, as I pointed out in another post on this thread in response to
@chatterbears, a utilitarian ethicist can accept that animals feel pain/pleasure but still conclude that eating them is ethically allowed provided that any pain their slaughter causes is outweighed by the utility derived from products created as a result of that slaughter. That is, there is at least one ethical system where arguments that it is morally acceptable to eat meat can easily be formulated.
Maybe you reject utilitarianism. Fine. But then you will have to argue for (1) why that whole system is flawed and (2) why any proposed alternative system is justifiable before you starting arguing about the morality of eating animal meat. Otherwise your arguments will simply be aimed at cross purposes with a significant number of relevant moral agents, i.e. utilitarians. (I should point out that not all utilitarians agree that animal exploitation is justified from a utilitarian perspective. Peter Singer, for example, advocates utilitarian reasons for vegetarianism. I don't think that changes the fact that animal consumption
can in theory be justified on utilitarian grounds.) The OP here was directed at the claim that there
are no moral or ethical justifications for eating meat. I believe I have provided at least one such justification in the form of utilitarianism, making the absolute claim posited in the OP false. None of the posts have given me any reason to think otherwise at this point.
A secondary issue for the pain/pleasure position is that (1) it would be obsolete provided we implemented pain free methods of animal husbandry, which seems entirely possible and (2) since it only would prevent a person from causing an animal pain in order to exploit the resulting meat for consumption, it does not absolutely prohibit humans from eating meat provided they were not the ones who caused the pain. That is, there would be no moral prohibition against eating fresh road kill, for example, or scavenging the meat freshly felled by other animals. In other words, even if pain/pleasure is what made animals relevant moral agents, that would not form the basis for an absolute moral prohibition against eating meat. Consequently, there is no universal justification for strict vegetarianism.