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.
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.
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 three 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.