Animal Liberation
Anyone who wants to get to the fundamentals of Justice beyond humans, further understand Speciesism, and see the one of the texts that started the animal rights movement.
“In the first edition of this book, I rejected this view on the grounds that it requires us to think that bringing a being into existence confers a benefit on that being—and to hold this, we must believe that it is possible to benefit a nonexistent being. This, I thought, was nonsense. But now I am not so sure. (My unequivocal rejection of this view is, in fact, the only philosophical point made in the earlier edition on which I have changed my mind.) After all, most of us would agree that it would be wrong to bring a child into the world if we knew, before the child was conceived, that it would have a genetic defect that would make its life brief and miserable. To conceive such a child is to cause it harm. So can we really deny that to bring into the world a being who will have a pleasant life is to confer on that being a benefit? To deny this, we would need to explain why the two cases are different, and I cannot find a satisfactory way of doing that.20…” (Peter Singer, Animal Liberation)
The argument of how to consider unborn beings is a tough one, as referenced here. How to appropriately consider future beings?
“If a calf, say, grazes on rough pasture land that grows only grass and could not be planted with corn or any other crop that provides food edible by human beings, the result will be a net gain of protein for human beings, since the grown calf provides us with protein that we cannot—yet—extract economically from grass.” (Peter Singer, Animal Liberation)
“The argument we are now considering raises the issue of the wrongness of killing—an issue which, because it is so much more complicated than the wrongness of inflicting suffering, I have kept in the background up to this point. Our brief discussion near the close of the first chapter, however, was enough to show that for a being capable of having desires for the future there may be something particularly bad about being killed, something that is not equaled by the creation of another being. The real difficulty arises when we consider beings not capable of having desires for the future—beings who can be thought of as living moment by moment rather than having a continuous mental existence. Granted, even here, killing still seems repugnant. An animal may struggle against a threat to its life, even if it cannot grasp that it has “a life” in the sense that requires an understanding of what it is to exist over a period of time. But in the absence of some form of mental continuity it is not easy to explain why the loss to the animal killed is not, from an impartial point of view, made good by the creation of a new animal who will lead an equally pleasant life.21” (Peter Singer, Animal Liberation)
“Assume that, improbable as it seems, researchers do turn up evidence suggesting that plants feel pain. It would still not follow that we may as well eat what we have always eaten. If we must inflict pain or starve, we would then have to choose the lesser evil. Presumably it would still be true that plants suffer less than animals, and therefore it would still be better to eat plants than to eat animals. Indeed this conclusion would follow even if plants were as sensitive as animals, since the inefficiency of meat production means that those who eat meat are responsible for the indirect destruction of at least ten times as many plants as are vegetarians! At this point, I admit, the argument becomes farcical, and I have pursued it this far only to show that those who raise this objection but fail to follow out its implications are really just looking for an excuse to go on eating meat.” (Peter Singer, Animal Liberation)
“For philosophers of the 1950s and 1960s, the problem was to interpret the idea that all human beings are equal in a manner that does not make it plainly false. In most ways, human beings are not equal; and if we seek some characteristic that all of them possess, then this characteristic must be a kind of lowest common denominator, pitched so low that no human being lacks it. The catch is that any such characteristic that is possessed by all human beings will not be possessed only by human beings. For example, all human beings, but not only human beings, are capable of feeling pain; and while only human beings are capable of solving complex mathematical problems, not all humans can do this. So it turns out that in the only sense in which we can truly say, as an assertion of fact, that all humans are equal, at least some members of other species are also “equal”—equal, that is, to some humans. If, on the other hand, we decide that, as I argued in Chapter 1, these characteristics are really irrelevant to the problem of equality, and equality must be based on the moral principle of equal consideration of interests rather than on the possession of some characteristic, it is even more difficult to find some basis for excluding animals from the sphere of equality.” (Peter Singer, Animal Liberation)
Good core of the argument for why animals must be considered alongside humans. Could probably parse out more from this. Any characteristic shared by all humans, is not only shared by humans