Here is an extract from Peter Singer's Practical Ethics.

The total view treats infants as replaceable, in much the same way as it treats non-self-conscious animals (as we saw in Chapter 5). Many will think that the replaceability argument cannot be applied to human infants. The direct killing of even the most hopelessly disabled infant is still officially regarded as murder; how then could the killing of infants with far less serious problems, like haernophilia, be accepted? Yet on further reflection, the implications of the replaceability argument do not seem quite so bizarre. For there are disabled members of our species whom we now deal with exactly as the argument suggests we should. These cases closely resemble the ones we have been discussing. There is only one difference, and that is a difference of timing – the timing of the discovery of the problem, and the consequent killing of the disabled being.

Prenatal diagnosis is now a routine procedure for pregnant women. There are various medical techniques for obtaining information about the fetus during the early months of pregnancy. At one stage in the development of these procedures, it was possible to discover the sex of the fetus, but not whether the fetus would suffer from haemophilia. Haemophilia is a sex- linked genetic defect, from which only males suffer; females can carry the gene and pass it on to their male offspring without themselves being affected. So a woman who knew that she carried the gene for haemophilia could, at that stage, avoid giving birth to a haemophiliac child only by finding out the sex of the fetus, and aborting all males fetuses. Statistically, only half of these male children of women who carried the defective gene would have suffered from haernophilia, but there was then no way to find out to which half a particular fetus belonged. Therefore twice as many fetuses were being killed as necessary, in order to avoid the birth of children with haemophilia. This practice was widespread in many countries, and yet did not cause any great outcry. Now that we have techniques for identifying haemophilia before birth, we can be more selective, but the principle is the same: women are offered, and usually accept, abortions in order to avoid giving birth to children with haemophilia.

The same can be said about some other conditions that can be detected before birth. Down's syndrome, formerly known as mongolism, is one of these. Children with this condition have intellectual disabilities and most will never be able to live in- dependently, but their lives, like those of small children, can be joyful. The risk of having a Down's syndrome child increases sharply with the age of the mother, and for this reason prenatal diagnosis is routinely offered to pregnant women over 35. Again, undergoing the procedure implies that if the test for Down's syndrome is positive, the woman will consider aborting the fetus and, if she still wishes to have another child, will start another pregnancy, which has a good chance of being normal.

Prenatal diagnosis, followed by abortion in selected cases, is common practice in countries with liberal abortion laws and advanced medical techniques. I think this is as it should be. As the arguments of Chapter 6 indicate, I believe that abortion can be justified. Note, however, that neither haemophilia nor Down's syndrome is so crippling as to make life not worth living, from the inner perspective of the person with the condition. To abort a fetus with one of these disabilities, intending to have another child who will not be disabled, is to treat fetuses as interchangeable or replaceable. If the mother has previously decided to have a certain number of children, say two, then what she is doing, in effect, is rejecting one potential child in favour of another. She could, in defence of her actions, say: the loss of life of the aborted fetus is outweighed by the gain of a better life for the normal child who will be conceived only if the disabled one dies.

When death occurs before birth, replaceability does not conflict with generally accepted moral convictions. That a fetus is known to be disabled is widely accepted as a ground for abortion. Yet in discussing abortion, we saw that birth does not mark a morally significant dividing line. I cannot see how one could defend the view that fetuses may be 'replaced' before birth, but newborn infants may not be. Nor is there any other point, such as viability, that does a better job of dividing the fetus from the infant. Self-consciousness, which could provide a basis for holding that it is wrong to kill one being and replace it with another, is not to be found in either the fetus or the newborn infant. Neither the fetus nor the newborn infant is an individual capable of regarding itself as a distinct entity with a life of its own to lead, and it is only for newborn infants, or for still earlier stages of human life, that replaceability should be considered to be an ethically acceptable option.

It may still be objected that to replace either a fetus or a newborn infant is wrong because it suggests to disabled people living today that their lives are less worth living than the lives of people who are not disabled. Yet it is surely flying in the face of reality to deny that, on average, this is so. That is the only way to make sense of actions that we all take for granted. Recall thalidomide: this drug, when taken by pregnant women, caused many children to be born without arms or legs. Once the cause of the abnormal births was discovered, the drug was taken off the market, and the company responsible had to pay compensation. If we really believed that there is no reason to think of the life of a disabled person as likely to be any worse than that of a normal person, we would not have regarded this as a tragedy. No compensation would have been sought, or awarded by the courts. The children would merely have been 'different'. We could even have left the drug on the market, so that women who found it a useful sleeping pill during pregnancy could continue to take it. If this sounds grotesque, that is only because we are all in no doubt at all that it is better to be born with limbs than without them. To believe this involves no disrespect at all for those who are lacking limbs; it simply recognises the reality of the difficulties they face.

In any case, the position taken here does not imply that it would be better that no people born with severe disabilities should survive; it implies only that the parents of such infants should be able to make this decision. Nor does this imply lack of respect or equal consideration for people with disabilities who are now living their own lives in accordance with their own wishes. As we saw at the end of Chapter 2, the principle of equal consideration of interests rejects any discounting of the interests of people on grounds of disability.

Even those who reject abortion and the idea that the fetus is replaceable are likely to regard possible people as replaceable. Recall the second woman in Parfit's case of the two women, described in Chapter 5. She was told by her doctor that if she went ahead with her plan to become pregnant immediately, her child would have a disability (it could have been haemophilia); but if she waited three months her child would not have the disability. If we think she would do wrong not to wait, it can only be because we are comparing the two possible lives and judging one to have better prospects than the other. Of course, at this stage no life has begun; but the question is, when does a life, in the morally significant sense, really begin? in Chapters 4 and 5 we saw several reasons for saying that life only begins in the morally significant sense when there is awareness of one's existence over time. The metaphor of life as a journey also provides a reason for holding that in infancy, life's voyage has scarcely begun.

Regarding newborn infants as replaceable, as we now regard fetuses, would have considerable advantages over prenatal diagnosis followed by abortion. Prenatal diagnosis still cannot detect all major disabilities. Some disabilities, in fact, are not present before birth; they may be the result of extremely pre- mature birth, or of something going wrong in the birth process itself. At present parents can choose to keep or destroy their disabled offspring only if the disability happens to be detected during pregnancy. There is no logical basis for restricting parents' choice to these particular disabilities. If disabled newborn infants were not regarded as having a right to life until, say, a week or a month after birth it would allow parents, in consultation with their doctors, to choose on the basis of far greater knowledge of the infant's condition than is possible before birth.
All these remarks have been concerned with the wrongness of ending the life of the infant, considered in itself rather than for its effects on others. When we take effects on others into account, the picture may alter. Obviously, to go through the whole of pregnancy and labour, only to give birth to a child who one decides should not live, would be a difficult, perhaps heartbreaking, experience. For this reason many women would prefer prenatal diagnosis and abortion rather than live birth with the possibility of infanticide; but if the latter is not morally worse than the former, this would seem to be a choice that the woman herself should be allowed to make.

Another factor to take into account is the possibility of adoption. When there are more couples wishing to adopt than nor- mal children available for adoption, a childless couple may be prepared to adopt a haemophiliac. This would relieve the mother of the burden of bringing up a haemophiliac child, and enable her to have another child, if she wished. Then the replaceability argument could not justify infanticide, for bringing the other child into existence would not be dependent on the death of the haemophiliac. The death of the haemophiliac would then be a straightforward loss of a life of positive quality, not outweighed by the creation of another being with a better life.

So the issue of ending life for disabled newborn infants is not without complications, which we do not have the space to discuss adequately. Nevertheless the main point is clear: killing a disabled infant is not morally equivalent to killing a person. Very often it is not wrong at all.