Singer not only holds that abortion is permissible at all stages of pregnancy, but also notoriously defends the view that there are circumstances in which it would be moral to kill a newborn child.In other words, pro-lifers argue that since there's no qualitative difference between the born infant and the unborn, and since killing the born infant is a moral wrong so, too, is killing the unborn. Singer, however, argues that since there's no difference between the born infant and the unborn, and since the unborn has no right to life, neither should the infant. Wick notes that:
Singer arrives at this position by running a familiar anti-abortion argument in reverse. The anti-abortion argument is that because a child does not undergo any transformation in the course of being born that could plausibly be supposed to give it a right not to be killed, the unborn have such a right, since to deny this would lead to the absurd conclusion that there is nothing inherently wrong in killing the newly born.
Singer reasons in the other direction and denies that both the unborn and the newly born have a right not to be killed.
Singer believes newborn infants are not yet persons because they lack the rationality and self-awareness required to possess a desire to go on living. It is the thwarting of that desire, rather than the taking of life as such, that he believes accounts for the wrongness of killing in those cases in which killing is wrong.There's much more on Singer's utilitarianism at the link and I recommend reading it. Wick is correct when he adds that:
In the most recent edition of Singer’s Practical Ethics, he writes that strict conditions should be placed on the circumstances in which infanticide is permitted, but “these restrictions should owe more to the effects of infanticide on others than to the intrinsic wrongness of killing an infant.”
This view shocks many, including many who admire Singer for his work on our duties to animals and the world’s poor. But his position is exactly the one that his utilitarian theory implies, and the way that he arrives at that position can serve to illustrate features of the utilitarian approach to ethics that make it attractive even to those who are reluctant to accept the conclusions that it implies.
One reason utilitarian ethical thinking proves so persistently attractive even to those who are reluctant to accept the conclusions it implies is that many of us have difficulty imagining what else ethical thinking could be.Of course, Singer is an atheist, and if he's right about there being no God then it's hard to imagine how anyone could argue that he's wrong about infanticide in particular and utilitarianism in general. The former follows from the latter, and in a godless world one ethical system is just as useful and defensible as another since they're all matters of arbitrary personal preference.
If a society spurns the notion of a transcendent moral authority which establishes right and wrong and to whom we are accountable then there's no reason to prefer utilitarianism over egoism. Utilitarianism says that we should maximize human well-being and happiness which means that when I act I should take into consideration how my act will affect the happiness of others, but, given atheism, why should I? Why should I care about the well-being of people I don't even know? Why should I not just care about my own happiness and well-being?
Moreover, once we realize that in a godless world egoism (the belief that my well-being is all that matters) is the default position there's no reason not to adopt an ethic of might-makes-right. There's certainly no reason to think that anyone who does adopt such an ethic is wrong to do so. If promoting my well-being is right then whatever I have the power to do is right to do as long as it makes me happy.
When God is banished from ethics, when the divine commands to love God and love our neighbor are deemed obsolete, then society will ultimately devolve to the ethics of the Roman Coliseum or Suzanne Collins' Hunger Games.
That's why it sounds so foolish when atheists like Singer make moral judgments about the treatment of animals or people. When an atheist asserts that X is wrong or immoral all he's saying is that he doesn't like X, but why should anyone care about what he likes? To that question the atheist can give no answer.