This is the first section of the paper I presented to the the Evangelical Philosophical Society Annual Meeting in Milwaukee two weeks ago. Several people have asked me to post it on MandM. It will appear as a two-part post series.
Christian theism has traditionally taught that human beings have equal dignity and worth, a moral status that separates them from non-human animals. Peter Singer has famously rejected this teaching, holding that human beings are not any more special than animals and doctrines of human dignity are indefensible. He contends that killing a new-born infant is, in and of itself, no more problematic than killing a non-human animal such as a cow or a pig and defends the permissibly of infanticide under certain conditions.
This paper will critically assess one important part of Singer’s position: his understanding of why it is wrong to kill. In I I will sketch Singer’s “desire account” of killing and its relationship to his own preference utilitarianism and project of animal equality. Following Don Marquis, I will argue in II, that this “desire account” is subject to important counter examples. In III I note Singer’s attempts to modify his position so as to avoid these counter examples and suggest that these modifications are problematic. In IV, I will suggest that, despite this, there is an important truth in Singer’s critique, one that Christian thinkers can appropriate in developing moral arguments for Christian theism.
I. Preference Utilitarianism and the desire account of the wrongness of killing
Classical Utilitarianism conjoins three theses. First, the maximisation thesis; an action is right if and only if it maximises overall net benefit: net benefit being the total amount of benefit accruing to individuals as a consequence of the action, minus any harms resulting. An action maximises net benefit when the consequences of performing it constitute a higher net benefit than that associated with any alternative action.
Second, , the thesis of equal consideration: a benefit or harm to any one individual is counted as having equal weight to a similar sized benefit or harm to any other individual.
Third, the thesis of hedonism: on this account, benefits and harms are understood in terms of pleasure and pain. Something benefits an individual or is good if it causes him pleasure and harms him if it causes pain.
Peter Singer is a preference utilitarian. Preference utilitarians accept both the maximisation and equal consideration theses however reject hedonism in favour of a desire fulfillment or preference satisfaction view of the good. Something is good for an individual if he desires or prefers it, and it is bad if contrary to his preferences or desires.
Singer uses preference utilitarianism to reject the doctrine that human beings have equal dignity and worth, a moral status that separates them from non-human animals. Sentient animals clearly have desires; they can suffer and feel pain and desire not to. The equal considerations thesis entails that in so far as these desires are similar to those of human beings the suffering of an animal must be considered equal with that of a human being.
However, in terms of actual as opposed to potential psychological capacities, some human beings have a comparable mental life to that of animals. A new born human infant’s psychology is primitive. David Boonin notes “by any plausible measure dogs, and cats, cows and pigs, chickens and ducks are more intellectually developed than a new born infant.”  This means that the desires of a new born infant are similar to those of other animals.
Singer illustrates this point in a discussion of animal experimentation.
If experimenters would not be prepared to use a human infant, then their readiness to use non-human animals reveals an unjustifiable form of discrimination on the basis of species, since adult apes, monkeys, dogs, cats, rats, and other animals are more aware of what is happening to them, more self-directing, and so are as far as we can tell, at least as sensitive to pain as a human infant. 
Singer grants that infants are often loved by their parents in a way in which other animals are not, and so experimenting on infants would contradict the desires of adult human beings. But antecedent to such desires is a preference for the interests of a human infant over that of an animal; this Singer considers merely an arbitrary and irrational bias in favour of our own species.
Racists violate the principle of [equal consideration] by giving greater weight to the interests of members of their own race when there is a clash between their interests and the interests of those of another race…Similarly, speciesists allow the interests of their own species to override the greater interests of other members of other species. The pattern is identical in each case 
Singer argues that facts about the suffering caused by factory farming, when conjoined with the equal considerations and maximisation theses entail a duty to become vegetarians. Whether this is correct is controversial and I will not go into this controversy today.
All I will note here is the implications for his position on human dignity. Singer notes his conclusion “differs strikingly from the prevailing attitude in our society” that human beings have a special equal dignity. “How is it”, he asks, that our society should have come to accept such an irrational position?“Our present attitudes date from the coming of Christianity” . Christians, Singer explains, believed all human beings were created in the image of God. “During the centuries of Christian domination of European thought, the ethical attitudes based on these doctrines became part of the unquestioned orthodoxy of European civilisation”  Singer offers no argument against these doctrines. He simply states they are “no longer generally accepted”  and instead proposes to explore belief in human dignity “as part of a broadly secular ethic” . He concludes:
Once the religious mumbo-jumbo surrounding the term ‘human’ has been stripped away, we may continue to see normal members of our species as possessing greater qualities of rationality, self-consciousness, communication and so on than members of any other species, but we will not regard as sacrosanct the life of every member of our species, no matter how limited its capacity for intelligent or even conscious life may be 
Singer’s rejection of human dignity and his preference utilitarianism have implications for the morality of killing. “According to preference utilitarianism, an action contrary to the preference of any being is, unless outweighed by contrary preferences, wrong. Killing a person who prefers to exist is therefore all else being equal wrong”  If an individual does not desire to live then unless some third party desires they do, killing them is not wrong. If we use the phrase “right to life” as shorthand for when killing someone is against their interests and so directly wrongs them, Singer’s position entails the desire account of killing:
Desire account: An organism has a right to life if and only if that organism has a desire to continue existing.
Singer’s advocacy of abortion and infanticide follows from the desire account of killing. A human infant, like an animal, is not a person: “a thinking, intelligent being that has reason and reflection and can consider itself as itself, the same thinking being, in different times and places.”  However only persons are aware of their own existence over time, and so only persons can desire to continue to exist. It follows then that “No infant – disabled or not – has as strong a claim to life as beings capable of seeing themselves as distinct entities, existing over time.” This has fairly radical implications: infants do not gain awareness of their future existence until around age two and even here personhood develops gradually; a strong desire to continue exist probably emerges even latter.
However, although they have no right to life and killing does not harm them, Singer emphasises that it doesn’t follow that killing infants is generally permissible.
“[T]he birth of a child is usually a happy event for the parents. They have, nowadays, often planned for the child. The mother has carried it for nine months. From birth, a natural affection begins to bind the parents to it” so usually killing an infant will be against the interests, desires or preferences of the parents or perhaps broader society.” 
In most cases infanticide will be contrary to the desires of parents and the broader society. However this is not always the case “It is different when the infant is born with a serious disability. Birth abnormalities vary, of course. Some are trivial and have little effect on the child or its parents; but others turn the normally joyful event of birth into a threat to the happiness of the parents, and any other children they may have.” 
Singer therefore concludes that, in those cases, where the parents or society do not desire an infant to live, it is permissible to kill infants. “the main point is clear, killing a disabled person is not morally equivalent to killing a person very often it’s not wrong at all”. This will happen he believes only when the child is disabled.
David Boonin A Defense of Abortion (Cambridge: Cambridge University Press, 2003) 121.
Peter Singer, “Tools for Research” in Writings on an Ethical Life ( Harper Collins: London, 2000) 52.
Peter Singer, “All Animals are Equal” in Writings on an Ethical Life ( Harper Collins: London, 2000) 35).
Singer, “What’s Wrong with Killing” in Writings on an Ethical Life ( Harper Collins: London, 2000) 35) 129.
Peter Singer, “Sanctity of Life or Quality of Life?” Paediatrics, 1983, 72:1, 128-9.
Peter Singer, “Whats Wrong with Killing” 134.
Ibid , 128.
Peter Singer, “Justifying Infanticide” in Writings on an Ethical Life ( Harper Collins: London, 2000) 187.