One interpretation of antinatalism is that it would be a desirable thing if all procreation were to stop now, and perhaps that it would be good if the human species were to go extinct very soon. Being something of a squish, I confess to being not-entirely-persuaded of the truth of either of these propositions.
People could be killed off or they could die off. One might imagine a “big red button” which, if pressed, would instantly and painlessly terminate all human life. Someone more ruthlessly utilitarian than I am would be tempted to push that big red button. But as it happens, there is no big red button. There are ways in which people die off in very large numbers, and perhaps these could be pressed to the point of extinction: global thermonuclear war, catastrophic global warming, the release into the human population of a genetically-engineered super disease organism. The suffering that would be occasioned by these events would be truly horrifying and widespread, even if they were relatively quick. They are not the sort of things any sane person, even one who thinks that extinction sooner rather than later is something to be welcomed, would contemplate.
If we suppose, as is not at all likely, that all procreation were to stop right now. Barring other events that were to accelerate our collective dying off, or the development of technologies that dramatically lengthen the human life span, that would bring about the complete extinction of the human race in about a century or so. If on the whole one thinks that the sooner-rather-than-later extinction of humanity is a good thing, that it might seem like such a decision to completely stop procreating is a good thing. But as David Benatar points on in Chapter Six of Better Never to Have Been., the experiences of the last generations of people before the hypothetical end in this scenario are likely to be pretty ghastly. At some point several decades from now the world would be inhabited by a few billion elderly people, with at best limited capacity for supporting themselves as they are consumed by the debilities of age. They would, in all likelihood, suffer terribly (including from hunger and disease) as the social and physical infrastructure of human life as they would be increasingly unable to maintain began to fall apart.
The mass suffering of billions cannot possibly be the right result for someone motivated by the ethical concern with human suffering that animates antinatalism to begin with, so that result seems like it can’t be right, which is why Benatar ends up defending instead a phased die-off of the human species, achieved through sustained long-term sub-replacement fertility. He admits — as I think he must — that the lives of the last people living will still be very bad, and that in the meantime there will be the creation of new lives in which there will be a fair amount of other suffering. It is at least plausible, though, that the aggregate suffering in a phased die-off will be substantially less than in a sudden die-off. (And it seems certain that the aggregate suffering will be less than simply a continuation of the human status quo that heads off for indefinite thousands of years into the future.)
Phased extinction also seems highly feasible in ways that sudden extinction does not. As I’ve recently noted, some advanced countries have already achieved significantly sub-replacement fertility, and I don’t think there’s any reason to think that this achievement cannot be replicated globally. It wouldn’t even require that most people be antinatalists — just that they might come to value the sort of lives that are possible to those who have few or no children.
But we must note that this path, while feasible, would not be quick. Doing some hasty spreadsheeting based on some data available from the United States Bureau of the Census, one can estimate the existence of about 2.5 billion people in the world who are either women under the age of 45, or girls. Suppose (very optimistically) that a crypto-antinatalist program were to succeed right now in reducing around the world fertility to the levels now seen in Japan, viz about 1.4 children per woman. We could then do some back-of-the-envelope calculations to watch the global human population decline over time.
Something worth noting is that it will be a rather long time in human terms. We would expect a human population still in the millions for at least twelve generations into the future, and at least in the thousands about 21 generations into the future. If we assume a mean time between generations of roughly 25 years, that means that there will be a lot of people still around for at least five centuries into the future.
That’s a number with significant policy implications if you care about preventing suffering. Since a lot of people will live in that future, even a curtailed one, it suggests to me that antinatalists ought to take a broad view about the necessity of preventing things like global ecological damage (e.g. through climate change), avoiding future wars, and other catastrophes that will cause vast suffering if they are allowed to happen. It also suggests to me that antinatalists shouldn’t take a fatalistic view or shrug off efforts to improve the quality of human life. On even optimistic projections about the future, there will be a lot of human life yet to come.