The Spartans had a tradition of discarding infants that were physically weak or deformed. When I was younger, I thought this practice is cruel and absolutely immoral. But nowadays I'm not so sure. In particular, I think to some extent, it may be actually merciful in that it spared those individuals living their life in the pain and humiliation of not being able to integrate into the society. After all, what is the point of living a life as a completely useless person no one respects or loves? In Spartan society, that was almost entirely based on one's ability to participate in military activities. Today it's different but there are certain cases where the situation is very much analogous. Is infanticide justifiable in any circumstances?
Ethicist Peter Singer defends infanticide in his books Should the Baby Live? and Practical Ethics. The following is an excerpt from an editorial in the Washington Post which quotes Singer's writings directly:
From "Practical Ethics": "Human babies are not born self-aware, or capable of grasping that they exist over time. They are not persons." But animals are self-aware, and therefore, "the life of a newborn is of less value than the life of a pig, a dog, or a chimpanzee."
Accordingly, from "Should the Baby Live?": "It does not seem wise to add to the burden on limited resources by increasing the number of severely disabled children."
Also in that book, Singer and his colleague, Helga Kuhse, suggested that "a period of 28 days after birth might be allowed before an infant is accepted as having the same right to live as others."
In "Practical Ethics," second edition, Singer makes clear that the parents, together with their physicians, have the right to decide whether "the infant's life will be so miserable or so devoid of minimal satisfaction that it would be inhumane or futile to prolong life."
As an example, he speaks of severe forms of spina bifida, which, he says, "can affect as many as one in 500 live births." He adds Down's syndrome, which also is not rare. Parents, by disposing of such infants, still may have a chance to have "another pregnancy, which has a good chance of being normal."
As you may imagine, these ideas are controversial. Christians, for example, have completely different notions of what constitutes a human person and also reject the utilitarian and consequentialist foundations of Singers' ethics. Advocates for the rights of disabled people also fear that Singer's arguments are dehumanizing and reinforce prejudice.
Infanticide, euthanasia, and the intrinsic value of human life
Your question focuses on infanticide but the considerations you advance in its favour show, or so it seems to me, that euthanasia is the real, the major issue here. Your infanticide is only a special case of euthanasia : that of terminating a life in the (supposed) interests of the euthanised because, on the grounds you specify, s/he 'cannot integrate into society' and hence is a 'completely useless person no one respects or loves'.
This is not to say (1) that to regard euthanasia as justifiable in certain circumstances - an issue on which I withhold my opinions - means that one supports infanticide but (2) I can't see how on the basis of your case for infanticide, you can avoid extension of infanticide to all cases of euthanasia where life is terminated for the benefit of the person euthanised on the grounds you specify.
Also, since Spartan infanticide involved no consultation with the children involved, it was involutary infanticide, which translates across to involuntary euthanasia where consent does not apply.
I fully accept that you do not advocate involuntary euthanasia across the board - or possibly, at all. My point is that I do not see how, on the logic of your argument for involuntary infanticide, there is any logically stopping point to prevent your argument's justifying involuntary euthanasia if (IF) on your grounds it justifies involuntary infanticide.
Note that this is not a 'slippery slope' argument. I am not suggesting that one thing will lead to another in the matter of killing other persons. I am deducing the logical implications of your argument - such as I take them to be.
My answer to your question is, then, a hypothetical : infanticide of infants whose lives are 'pointless', who have as some might say no quality of life, is justified if involuntary euthanasia on the grounds of your argument is justified. I said I would keep my own opinions back. I cannot but add, however, that I do not think a person's, an infant's or other's, pain, illness or disability as such makes their life 'pointless'. Nor do I see why they should not be 'respected or loved' and in that sense 'integrated into society'.
This has back of it, I suppose, a view of human life as having intrinsic value - of a human life as being 'pointful', or capable of being so, even in extremely disadvantageous conditions; and as attracting love and respect regardless of pain, illness or disability. What I've said does not logically depend on this view but fits well with it.
Infanticide and the extrinsic value of human life
A quite different view is possible and has been historically influential at a philosophical level. This is that the person, the individual, has no intrinsic but only instrumental or external value as part of an organism.
The state or society as an organism
H.J. McCloskey refers to organicists who argue that
if the state is an organism [which it is on this organicist view: GT], it is therefore both ontologically higher and more valuable than its parts, and such that the parts can be understood and valued only as parts of their organic whole, and, further, that the whole, being an organism, cannot be a means or instrument to some further end. (H. J. McCloskey, 'The State as an Organism, as a Person, and as an End in Itself', The Philosophical Review, Vol. 72, No. 3 (Jul., 1963), pp. 306-326: 307.)
Organicism comes in varieties. J.M.E. McTaggart argued vigorously whatever the case may be for regarding Hegel as an organic theorist - not, he thinks, the most accurate label - Hegel did not hold that persons have value solely as parts of an organic whole. But the view that McCloskey outlines has been held; and someone who holds it might regard as 'social surgery' (Collected Essays, Oxford: Clarendon, 1935.: 152) the removal of defective parts through infanticide or other means.
The view of human life as having not intrinsic but only instrumental, external value may not sit comfortably with prevailing Western values but it has a philosophical pedigree and so cannot be neglected here, whatever may be thought of it.
F.H. Bradley, Collected Essays, Oxford: Clarendon, 1935.
H. J. McCloskey, 'The State as an Organism, as a Person, and as an End in Itself', The Philosophical Review, Vol. 72, No. 3 (Jul., 1963), pp. 306-326.
J.M.E, McTaggart, 'The Conception of Society as an Organism', Studies in Hegelian Cosmology, Cambridge : CUP, 1901.
Is infanticide justifiable in any circumstances?
This is just a cost benefit evaluation.
There is nothing radically special about killing kids as opposed to adults. And so you could've asked to the same effect "is murder justifiable in any circumstances?".