Michael Huemer's article on abortion starts out with this framing of the debate:
Very few people think either that all fetuses have a right to life from the moment of conception, or that no fetuses have a right to life even one second before birth. Almost everyone has some intermediate position. Which means… [whether fetuses have a right to life] becomes, for most, a line-drawing question; most "pro-life" people are people who draw the line relatively early, while "pro-choice" people draw it relatively later.
This is a misrepresentation of the debate. Most pro-life groups argue that all fetuses have a right to life from the moment of conception. Just look at the position of the Catholic Church as an example of this view. It is not accurate to say that most pro-life people draw a line "relatively early". To view the debate as a line-drawing exercise means that one has already conceded that there is a point before the line at which abortion is legitimate. This is precisely what most pro-life people deny: they reject the legitimacy of abortion outright.
The line-drawing exercise that Huemer is describing is really the debate among pro-choice intellectuals. Pro-choice advocates do have to argue about where to draw an arbitrary line because any defender of abortion must address the question of until what point they think abortion is legitimate.
It is also very odd for Huemer to frame the debate in terms of what most people believe. Why should he be guided by what most people believe? Surely the decisive question for a philosopher like him is what are the best arguments on either side of this debate? Huemer wrote a book making the case that political authority is illegitimate. Should he have saved himself the trouble since very few people believe that argument?
Having misrepresented the terms of the debate, Huemer also misrepresents the basic pro-life argument. Huemer states:
Some say that the moment of conception is special, because it is at that point that there is first an entity with a genuine potential to become a person. But this is not true. An egg cell and a sperm cell, where the sperm cell is swimming toward the egg, also have the potential to become a person.
This is a straw man. The basic pro-life argument is that conception is the beginning of a human being's life, and all human beings have a right to life, therefore abortion cannot be justified. This is a well-known argument and whether or not he agrees, he ought to at least represent it fairly. Instead, Huemer couches his "potential to become a person" argument in the same language that pro-choicers adopt in their own internal debate. It is pro-choicers who talk about when to recognise personhood, by which they mean when to recognise that a human being has rights. Pro-lifers argue that all humans have rights. Huemer's counter-arguments to this straw man are therefore irrelevant. Gametes are not human beings, zygotes and fetuses are.
Huemer presents his article as a review of both sides of the abortion debate, but he fails to engage with any pro-life philosophers. While he directly addresses the arguments of pro-choice philosophers such as Tooley and Thomson, he does not cite a single pro-life philosopher. Instead, he creates his own version of pro-life arguments which, as discussed in the conception example, are weak. The basic pro-life argument about conception discussed above is made clearly in the article Abortion: The Moral Status of the Unborn by philosopher Richard Werner. Huemer should have responded to Werner rather than setting up his own straw man to respond to.
Another pro-life argument that he does not address properly is the question of the compatibility of abortion with parental obligations. Huemer states:
Many people think that parents have special obligations to their children, such that you would have to do much more to save your child than you would have to do to save a stranger. Does this mean that a mother has special obligations to her fetus?
This is a perfunctory treatment of a very important argument. It is not that "you would have to do much more to save your child than you would have to do to save a stranger", rather it is that parents have acquired an enforceable positive obligation towards their child based on their causal role in placing the child in a state of peril. Failure to remove the child from peril constitutes an act of aggression. This means parents have a legitimate enforceable positive obligation to protect the child, whilst they have no such enforceable obligation to strangers. Abortion is completely incompatible with this obligation.
This argument was dealt with in depth by Doris Gordon, a fellow libertarian whose work Huemer should know but whom he doesn't address. She made a range of secular pro-life arguments which were inspired by and grounded in her realisation of the fundamental incompatibility of abortion with parental obligations. Huemer also doesn't attempt to rebut the argument from parental obligations, he just leaves it hanging as an open question. Does he agree with the argument? If not, why?
We have seen that Huemer fails to represent pro-life arguments properly and therefore does not engage with them. What about his treatment of pro-choice arguments? Here he does address various problems with arguments made by leading pro-choice philosophers. But he fails to address the most important problem: every argument used to justify abortion also justifies infanticide. This is an issue openly recognised by the more consistent pro-choice philosophers. Some, like David Boonin, just uncomfortably acknowledge the problem and move along swiftly. Others, like Michael Tooley and Peter Singer, choose to bite the bullet and accept that one cannot deny the legitimacy of infanticide if one accepts the legitimacy of abortion. If Huemer wants to argue that the abortion question is difficult then he should have addressed the most difficult issue pro-choicers face.
Huemer argues that the abortion debate is "difficult" because the legitimacy of abortion is a "subtle, complex question" that is "highly intellectually interesting". I agree with Huemer that the debate about abortion is difficult, but not for the reasons he states. I think it is difficult because abortion is deeply ingrained into Western culture, yet what is being debated is whether this widespread practice constitutes the murder of innocent children. This debate makes people incredibly uncomfortable because it is a moral question with enormous personal consequences, not because it is "intellectually interesting" and "subtle".
For libertarians in particular, abortion is difficult because if you accept that it is not justifiable then you must accept that the widespread practice of abortion represents by far the worst violation of the nonaggression principle in the world today, far worse than any government program, yet most libertarians do not speak out against it.
Another thing that makes this debate difficult for someone like Huemer is that, among the intelligentsia, there is in fact no debate on abortion, there is only one socially acceptable opinion. Being explicitly pro-life is more likely to get you ostracised in academia than being an anarchist will. As Brad Stetson described in The Silent Subject: Reflections on the Unborn in American Culture:
Civilized and thoughtful people are expected to step around the violent death of the unborn accomplished by every abortion. To mention it in dialogue or debate is to solicit angry glares, impatient sighs and apparently learned expressions of skepticism about knowing when "human life begins." … There is no such thing, in the agora of public opinion, as being compassionate to the unborn. Not only are they not accorded the legal status of persons, but they are not even admitted into public discourse as legitimate objects of concern.
At least Huemer does not actively defend abortion, which makes him unusual among libertarian academics. Yet instead of taking a position, he counsels against strong views, suggesting that certainty would mark one as a "dogmatic ideologue" unable to appreciate a "subtle, complex question." On one level this reluctance sounds like philosophical caution; on another, it sounds like an excuse for avoiding taking a stand against a profound injustice.