In the fifth chapter of the book Benatar offers his argument for abortion, a ‘Pro-Death’ View as he calls it.
Basically the idea is that since coming into existence is harmful, and since at least during the earlier stages of pregnancy, one has not yet come into existence in the morally relevant sense, people mustn’t give a justifiable reason for having an abortion but for not having one.

It is the failure to abort which must be defended he argues, and adds that the greater the harm of existence, the harder it will be to defend that failure. And if life is as bad as he suggests it is – then the failure to abort (at least during the earlier stages of pregnancy) may never, or almost never, be justified.

I agree that people mustn’t give a justifiable reason for having an abortion but for not having an abortion, only for different reasons than Benatar’s. His first premise – that the creation of a new person is always harmful – is correct, but as opposed to what Benatar means when he claims that, the creation of a new person is always harmful first and foremost for other sentient creatures who would be harmed by that new person. And harming them can never be justified.
The harms to others are so severe that it nullifies the harm of abortion even when performed after the fetus has already reached the morally relevant stage. Arguing otherwise is suggesting that the interest of a fetus, even if already conscious, is more important than the interests of all the existing sentient creatures who would be harmed if that person is born. That is morally wrong.

Considering the harms to others and not having an abortion could never be justified, and considering how severe the harms to others are, abortion at any stage is always morally justified.

Some argue that abortion is wrong since it deprives a person of the value of its future. But such an argument forces us to think that it would be worse to kill a fetus than to kill a thirty-year old, since a fetus, all things being equal, would have a longer future, and would therefore be deprived of more. Most people find that preference unacceptable. Benatar provides an explanation why:

“The greater deprivation makes sense when we are comparing the death of a thirty-year old with that of a nonagenarian, where most people take the former to be worse. However, it makes much less sense when comparing the deaths of the fetus and the thirty-year old, where many of us take the latter to be much worse. The best explanation for this is that a fetus has not yet acquired the interest in its own existence that the thirty-year old has.
The case of the thirty-year old and the nonagenarian can be explained in one of two ways. It could be that both have equal interests in continued life but the nonagenarian has less life left. Alternatively, in some cases only, it could be that the nonagenarian’s interest in living has already begun to decline, perhaps on account of life’s becoming worse with advancing age and decrepitude.” (p.159)

There is another reason to prefer abortion over killing a thirty-year old, and that is since the latter had already passed 30 years of causing suffering, while the fetus still has a lifetime of inflicting suffering on others. The main ethical reason to prefer killing the fetus over a thirty-year old is the time each has left to harm others. All things being equal, the fetus has 30 years more to inflict harms, so there is no dilemma.
Even if we look at it from Benatar’s view and not from the harm to others view, if life is as bad as he claims it is, then clearly it is better to kill the fetus who has a lifetime of suffering ahead, while the thirty-year old at least has 30 years less to suffer.

Having said that, Benatar nevertheless seriously argues for a right to procreate:

“If a right to reproductive freedom were withheld in order to prevent harm to those who would be brought into existence, the state could then either simply let people exercise reproductive choices without having a right to do so, or it could actively prohibit reproduction. The first option would be pointless. If the point of withholding an entitlement to have children is to prevent the harm of bringing people into existence, why withhold an entitlement to have children only then to permit people to have children?
Withholding the right would have to bfocusing on the harms to humans[r1]
[r1]Link to 1e linked, therefore, to a prohibition on having children. However the argument in defence of a legal right to reproductive freedom might go, procreative prohibition simply would not work. People would find ways of breaking the law. To enforce the law, even partially and unevenly, the state would have to engage in highly intrusive policing and the invasions of privacy that that would entail. On the plausible assumption that coitus itself should not and cannot effectively be prohibited, the state would have to be able to distinguish between those, on the one hand, who conceived wittingly or negligently, and those, on the other hand, who conceived accidentally. In either case, the state would then have to require abortions. In the case of the unwilling, this would require physically restraining people and performing unwanted abortions on them. The threat of this would very likely drive pregnancy underground, with women gestating and giving birth on the quiet. This, in turn, would very likely increase pregnancy- and parturition-related morbidity and mortality. These sorts of moral costs are immense and there is a powerful case to be made for the view that they are not outweighed by the benefits. This is particularly so given that the full benefits are unlikely to be obtained, given that much procreation would not be prevented by a prohibition on producing children.” (p.106)

It is strange that despite his claim in chapter 2 that it is always better never to have been, and despite his claim in chapter 3 that coming into existence is a very serious harm, he makes such an argument. Earlier in the book he also argues against that parents with dependents are somehow thought to count for more: “If, for example, there is some scarce resource—a donor kidney perhaps—and of the two potential recipients one is a parent of young children and one is not, the parent, all things being equal, will likely be favoured. Increasing one’s value by having children might be like increasing one’s value by taking hostages. We might find it unfair and decide not to reward it.” (p.12) Isn’t it a similar case when the right to procreate is justified by the fear of an Orwellian surveillance? If he can that easily defend the right to procreate doesn’t it significantly enfeebles the validity of his basic arguments? If life is as bad as he claims it is, can a surveillance society, as bad as it is in itself (and it most definitely is terrible) be compared with the harms of life? Even without considering the harms to others it is highly doubtful. And when considering the billions of sentient creatures being imprisoned for their entire lives, when considering the billions of sentient creatures being genetically modified so they would provide the maximum meat possible for the to-be born persons, when considering the billions of sentient creatures being forced to live without their family for their entire lives, when considering the billions of sentient creatures who suffer from chronic pain and maladies, when considering the billions of sentient creatures that can never breathe clean air, walk on grass, bath in water, and eat their natural food, when considering the billions of sentient creatures being violently murdered so the to-be born could consume their bodies, when considering the billions of sentient creatures whom their habitats are being destroyed and polluted, when considering the billions of sentient creatures being skinned alive, castrated, burned, poisoned, kicked, dehorned, detailed,  mounted, chained, experimented on, enslaved, it is totally unquestionable.
How can a life of extreme suffering ever be compared with outlawing procreation? Or even forced abortion? Can anything be compared with lifelong suffering with not even one painless second?

Don’t get this wrong, I agree that procreative prohibition won’t work completely, and I agree that it has tremendous moral costs, however, one must be extremely speciesist to think that they are not outweighed by the benefits. This is another problem with focusing on the harms to humans, when considering the harms to others there is no doubt what must be done.
Benatar himself mentions something of this sort as a solution to the expected problems involved in procreative prohibition:

“We can certainly imagine a society in which non-procreation could be widely (even if not universally) ensured without the invasions of privacy and bodily intrusions described above. This would be so if a safe, highly effective contraceptive substance could be widely administered without the knowledge of the population or the consent of individual people—in the drinking water, for example, or by aerial spray. A state in which this were done would avoid the horrendous image of Orwellian surveillance, or forced sterilizations and abortions, and so on. Of course, it would still be violating personal autonomy, but this, we have already seen, is not sufficient to make the case for a legal right to produce children.” (p.107)

With that I couldn’t agree more. It is much more likely to work, and it avoids the harms of procreative prohibition. It also doesn’t require a broad consent or state intervention or operation. All it takes is highly devoted activists with the right idea and resourcefulness, and hopefully finally the cruelest species ever would gradually go extinct, along with all the suffering it is forced to endure, and all the suffering it inflicts on others.

References

Benatar, D. Better Never to Have Been (Oxford: Oxford University Press, 2006)

Benatar, D.. Every Conceivable Harm: A Further Defence of Anti-Natalism
S. Afr. Journal Philos. 2012, 31

Benatar, D. Still Better Never to Have Been: A Reply to (More of) My Critics
Journal of Ethics (2013)

Feldman, F. Some puzzles about the evil of death in Life, Death and Meaning (Lanham MD: Rowman & Littlefield 2004)

Luper, S. Annihilation in Life, Death and Meaning (Lanham MD: Rowman & Littlefield 2004)

Pitcher, G. The misfortunate of the dead in Life, Death and Meaning (Lanham MD: Rowman & Littlefield 2004)

Rosenbaum, S. How to be dead and not to care in Life, Death and Meaning (Lanham MD: Rowman & Littlefield 2004)

Suits D. B. Why death is not bad for the ones died in Life, Death and Meaning (Lanham MD: Rowman & Littlefield 2004)