Dear Professor Singer:
American children are part of the American community, as a matter both of law and of love. We think it is better for them and for the society as a whole that they should be in school rather than working. We do not consider them income-earning assets of their parents. This has become a deep moral intuition in our society; it is also supported by pragmatic arguments. A more difficult question is whether, by refusing to import goods made with child labor, we should try to coerce foreign countries to adopt our moral norms. Child labor used not to be considered wrong, but that was at a time when few people received an education and when widespread poverty required that all able-bodied persons, of whatever age, be put to work. To the extent that these conditions continue to obtain in Third World nations, it is not obvious that we maximize utility (to use your preferred criterion of social welfare) by seeking to stamp out child labor through boycotts of goods made with it. And I am surprised that you treat as normative what "the majority consider desirable"; for the majority also desire to eat meat.
But all that is an aside. The principal issue you raise is the role of ethical argument. You ask how one can argue against racism in a "deeply racist" society. My answer is, by pointing to whatever fallacious beliefs undergird its racism. If its racism rests not on false beliefs but on material interest, argument will be impotent. There was plenty of argument against Negro slavery before 1861, but it took a Civil War to end the practice.
You ask how it is that our moral norms regarding race, homosexuality, nonmarital sex, contraception, and suicide have changed in recent times if not through ethical argument. This is a large question to which I cannot do justice in the space allotted me. But let me note, first, that philosophers have not been prominent in any of the movements to which you refer. Thurgood Marshall, Earl Warren, and Martin Luther King Jr. had a lot more to do with the development of an antidiscrimination norm than any academic; and the most influential feminists, such as Betty Friedan and Catharine MacKinnon, have not been philosophers either. As far as our changing attitudes toward sex are concerned, the motive forces were again not philosophical or, even, at root, ideological. They were material. As the economy shifted from manufacturing (heavy, dirty work) to services (lighter, cleaner), as contraception became safer and more reliable, as desire for large families diminished (the substitution of quality for quantity of children), and as the decline in infant mortality allowed women to reduce the number of their pregnancies yet still hit their target rate of reproduction, both the demand for women in the labor market and the supply of women in the labor market rose. With women working more and having as a consequence greater economic independence, they demanded and obtained greater sexual independence as well. Nonmarital, nonprocreative sex, including therefore homosexual sex, began to seem less "unnatural" than it had. At the same time, myths about homosexual recruitment were exploded; homosexuality was discovered to be genetic or in any event innate rather than a consequence of a "life style" choice; and so hostility to homosexuals diminished. The history of our changing sexual mores is more complex than this, but this sketch will give a flavor of how I prefer to explain social change. Ethical argument plays no role in the explanation.
You say that some readers of Animal Liberation have been persuaded by the ethical arguments in the book, and not just by the facts and the pictures. But if so, it is probably so only because these readers do not realize the radicalism of the ethical vision that powers your view on animals, an ethical vision that finds greater value in a healthy pig than in a profoundly retarded child, that commands inflicting a lesser pain on a human being to avert a greater pain to a dog, and that, provided only that a chimpanzee has 1 percent of the mental ability of a normal human being, would require the sacrifice of the human being to save 101 chimpanzees. If Animal Liberation had emphasized these implications of your utilitarian philosophy, it would have had many fewer persuaded readers; and likewise if it had sought merely to persuade our rational faculty, and not to stir our empathetic regard for animals.
Richard A. Posner