Any author who writes about the philosophy of the family long enough ends up conceding the principle that parents have causal responsibility for their children. This principle is so undeniable that even those who oppose it cannot help eventually making the argument for it in spite of themselves. Here are some examples.
Judith Jarvis Thomson
Judith Jarvis Thomson's highly influential Defense of Abortion was based on the argument that parents have no causal positive obligations, they may only have voluntarily accepted obligations:
Surely we do not have any such "special responsibility" for a person unless we have assumed it, explicitly or implicitly. If a set of parents do not try to prevent pregnancy, do not obtain an abortion, but rather take it home with them, then they have assumed responsibility for it, they have given it rights, and they cannot now withdraw support from it at the cost of its life because they now find it difficult to go on providing for it. But if they have taken all reasonable precautions against having a child, they do not simply by virtue of their biological relationship to the child who comes into existence have a special responsibility for it.
This argument by Thomson was highly influential on Rothbard, Brake, and many other opponents of causal parental obligation. Yet in the very same article, Thomson concedes the principle that parents have causal responsibility for the children that they create (at least in some cases):
Suppose a woman voluntarily indulges in intercourse, knowing of the chance it will issue in pregnancy, and she does become pregnant; is she not in part responsible for the presence of the unborn person inside her? No doubt she did not invite it in. But doesn’t her partial responsibility for its being there itself give it a right to the use of her body? … there are some cases in which the unborn person has a right to the use of its mother’s body, and therefore some cases in which abortion is unjust killing. There is room for much discussion and argument as to precisely which, if any. At any rate the argument certainly does not establish that all abortion is unjust killing.
Having conceded the principle of causal parental obligation, Thomson's fallback objection is that it does not apply in all cases. Not only does she completely avoid the most essential question (what determines the exceptions?) but she tries to reverse the burden of proof by arguing that since abortion may not be unjust killing in all cases, therefore abortion is justified. On the contrary, since she has conceded that any given abortion may be unjust killing, it must therefore be considered prima facie illegitimate unless proven otherwise. Mary Meehan's hunter analogy illustrates the fallacy of Thomson's line of argument:
Hunters notice movement in a thicket, but don’t know whether it is caused by a deer or another human being. If they shoot without determining the facts, and kill a human, they are guilty of homicide. Many abortion supporters say they cannot find out, yet they are willing to shoot anyway.
Murray Rothbard
Murray Rothbard argued that parents have no enforceable obligations to their children, on the grounds that the combination of creating someone and them being helpless does not generate obligation. Yet he clearly set out the case for parental obligation based on responsibility for creating a child who is (as a result of being created) placed in a state of helplessness:
The moral duty or responsibility of the parents to their children stems also from their act of voluntary creation, from their responsibility for bringing helpless babies into the world. Their moral responsibility is to raise these children, to bring them from their natural state of infant dependency to the status of rational, self-owning, independent adults. Their moral responsibility is to rear the children to the status of independence. What, then, does this imply? It implies caring, provision of food, shelter, education, etc., to the best of the parents' love and ability.
When Rothbard used the words "moral" duty, he meant by this that the obligation is not enforcible. By this he means that it is a matter of personal virtue only. Why should this be only a moral duty and not an enforcible one? Rothbard does not explain. If you remove the word moral, Rothbard has set out the case for enforcible parental obligations.
Elizabeth Brake
Elizabeth Brake is one of the main advocates for the theory that parental obligations arise only as a result of voluntary acceptance, and not as a result of actions taken by the parents. Yet in setting out her case, Brake concedes the causal argument. She accepts that procreation creates obligations (she calls these "procreative costs"). She argues that since what she calls "procreative costs" may not be identical to the parental obligations that are socially accepted by modern American culture, this proves that parental obligations are not created by the causal actions of the parent. It proves nothing of the sort.
Brake thinks the decisive argument is whether or not causal responsibility would give rise to the same conventional obligations as those in any particular culture. On the contrary, the point is that the causal responsibility of parents gives rise to an objective standard for obligations. It doesn't matter what the particular fashions are for parental behaviour towards children. Cultural conventions can include all sorts of acts by parents that are philosophically unjustifiable, for example circumcising infants. What matters is the objective requirement of the child to be removed from peril by being raised to self-sufficiency in adulthood. Parental obligations are as extensive as necessary to meet that objective requirement, including a child's psychological needs such as love, affection, attention, safe boundaries, encouragement etc. Yet they would also exclude all local conventions that cannot be objectively justified.
Since Brake's objection that causal parental obligations might not map exactly onto local conventions is irrelevant, what is left is her admission that the principle of causal obligations itself is valid. Brake accepts parental "obligations entailed by moral responsibility for a child's existence". She concedes that "parental obligations arise… for having placed the child in a needy situation in which its right to a minimally decent life is threatened". The fact that she chooses her own terminology of "procreative costs" is immaterial. She has accepted the basic principle that parents do have responsibility for the consequences of their actions, regardless of their intentions.
Having accepted this causal principle, Brake's own logic should compel her to reject the validity of abortion, since abortion is incompatible with such obligations. Yet she accepts both parental obligations and abortion. Such a clear contradiction can only be maintained if one is to take the position that parents have not yet caused a child to exist until they decide not to abort the child. This is to pursue motivated reasoning into the realm of absurdity.
Roderick Long
Roderick Long is another opponent of the causal responsibility of parents. Like Brake, Long argues that parental obligations can only be voluntary. Yet he also sets out the causal argument. In creating a child, the parents have put him in mortal danger and this is why parenting is a positive obligation resulting from causal action. Long concedes the principle that if someone puts another in danger and fails to act, that would be a homicide, so he concedes the existence of an obligation created in this way:
If S voluntarily places O in a situation where S’s failure to take positive action on O’s behalf will result in O’s death, then such a failure on S’s part is a killing, not merely a letting-die.”
He acknowledges that one may acquire positive obligations as a result of the consequences of one's actions, even if those consequences were unintended:
negative rights generate derivative positive rights. If you (intentionally or accidentally) take my umbrella, you acquire an enforceable obligation to take positive steps to return it to me
He also sets out the case for how enforceable positive obligations can arise by the creation of peril:
suppose Frieda is careening around the corner in her Lamborghini and suddenly sees Roscoe ambling across the road a short distance ahead. At her current speed, she has only two choices: (a) she can run over Roscoe, or (b) she can swerve around him. Running over Roscoe would be a violation of his negative rights; so Frieda has an enforceable obligation not to run over him. In the circumstances, what that amounts to is an enforceable obligation to swerve around him. But that obligation is not an obligation to sit back and do nothing; it is an obligation to take positive action, and a very specific positive action at that: she must turn the steering wheel in order to avoid running over Roscoe. Here we have a case, then, in which Frieda has an enforceable obligation to take positive action on Roscoe’s behalf – but only because that is the only way she can avoid violating her negative obligation not to treat Roscoe as a mere means. Roscoe’s right against Frieda not to be run over has generated, in the circumstances, a further right against her that she turn the wheel in a certain way.
This logic applies directly to parents. If a man and a woman engage in consensual sex and create a child, whether they intended to or not they have changed the state of the universe from one in which no child was in mortal peril to one in which a child is in mortal peril. They are thereby just as obliged to remove the child from peril as Long's Lamborghini driver is obliged to avoid hitting the pedestrian.
These authors all oppose the principle of causal parental obligations even though they also inadvertently set out the argument for it. They oppose it because they are engaged in motivated reasoning. All four authors understand that accepting the principle of parental obligations is incompatible with abortion. They consider a defence of abortion to be a core principle, so they refuse to accept the principle of causal parental obligations. Even when they make the argument for it despite themselves.