Dear Professor Singer:
I am impressed by your lucid and forceful argument for changing the ethical status of animals; and there is much in it with which I agree. I agree, for example, that human beings are not infinitely superior to or infinitely more valuable than other animals; indeed, I am prepared to drop "infinitely." I agree that we are animals and not ensouled demi-angels. I agree that gratuitous cruelty to and neglect of animals is wrong and that some costs should be incurred to reduce the suffering of animals raised for food or other human purposes or subjected to medical or other testing and experimentation.
But I do not agree that we have a duty to (the other) animals that arises from their being the equal members of a community composed of all those creatures in the universe that can feel pain, and that it is merely "prejudice" in a disreputable sense akin to racial prejudice or sexism that makes us "discriminate" in favor of our own species. You assume the existence of the universe-wide community of pain and demand reasons why the boundary of our concern should be drawn any more narrowly. I start from the bottom up, with the brute fact that we, like other animals, prefer our own—our own family, the "pack" that we happen to run with (being a social animal), and the larger sodalities constructed on the model of the smaller ones, of which the largest for most of us is our nation. Americans have distinctly less feeling for the pains and pleasures of foreigners than of other Americans and even less for most of the nonhuman animals that we share the world with.
Now you may reply that these are just facts about human nature; that they have no normative significance. But they do. Suppose a dog menaced a human infant and the only way to prevent the dog from biting the infant was to inflict severe pain on the dog—more pain, in fact, than the bite would inflict on the infant. You would have to say, let the dog bite (for "if an animal feels pain, the pain matters as much as it does when a human feels pain," provided the pain is as great). But any normal person (and not merely the infant's parents!), including a philosopher when he is not self-consciously engaged in philosophizing, would say that it would be monstrous to spare the dog, even though to do so would minimize the sum of pain in the world.
I do not feel obliged to defend this reaction; it is a moral intuition deeper than any reason that could be given for it and impervious to any reason that you or anyone could give against it. Membership in the human species is not a "morally irrelevant fact," as the race and sex of human beings has come to seem. If the moral irrelevance of humanity is what philosophy teaches, and so we have to choose between philosophy and the intuition that says that membership in the human species is morally relevant, then it is philosophy that will have to go.
Toward the end of your statement you distinguish between pain and death and you acknowledge that the mental abilities of human beings may make their lives more valuable than those of animals. But this argument too is at war with our deepest intuitions. It implies that the life of a chimpanzee is more valuable than the life of a human being who, because he is profoundly retarded (though not comatose), has less mental ability than the chimpanzee. There are undoubtedly such cases. Indeed, there are people in the last stages of Alzheimer's disease who, though conscious, have less mentation than a dog. But killing such a person would be murder, while it is no crime at all to have a veterinarian kill one's pet dog because it has become incontinent with age. The logic of your position would require treating these killings alike. And if, for example, we could agree that although a normal human being's life is more valuable than a normal chimpanzee's life, it is only 100 times more valuable, you would have to concede than if a person had to choose between killing one human being and 101 chimpanzees, he should kill the human being. Against the deep revulsion that such results engender the concept of a transhuman community of sufferers beats its tinsel wings ineffectually.
What is needed to persuade us to alter our treatment of animals is not philosophy, let alone an atheistic philosophy (for one of the premises of your argument is that we have no souls) in a religious nation, but to learn to feel animals' pains as our pains and to learn that (if it is a fact, which I don't know) we can alleviate those pains without substantially reducing our standard of living and that of the rest of the world and without sacrificing medical and other scientific progress. Most of us, especially perhaps those of us who have lived with animals, have sufficient empathy for the suffering of animals to support the laws that forbid cruelty and neglect. We might go further if we knew more about animal feelings and about the existence of low-cost alternatives to pain-inflicting uses of animals. And so to expand and invigorate the laws that protect animals will require not philosophical arguments for reducing human beings to the level of the other animals but facts, facts that will stimulate a greater empathetic response to animal suffering and facts that will alleviate concern about the human costs of further measures to reduce animal suffering.
Richard A. Posner