The procreation asymmetry can be formulated this way (due to Jeff McMahan):
while the fact that a person’s life would be worse than no life at all … constitutes a strong moral reason for not bringing him into existence, the fact that a person’s life would be worth living provides no (or only a relatively weak) moral reason for bringing him into existence.
This is a summary of the argument for the procreation asymmetry here and in the comments, especially this comment, which also looks further at the case of bringing someone into existence with a good life. I think this is an actualist argument, similar to Krister Bykvist’s argument in 2.1 (which cites Dan Brock from this book) and Derek Parfit’s argument on p.150 of Reasons and Persons, and Johann Frick’s argument (although his is not actualist, and he explicitly rejects actualism). The starting claim is that your ethical reasons are in some sense conditional on the existence of individuals, and the asymmetry between existence and nonexistence can lead to the procreation asymmetry.
1. From an outcome in which an individual doesn’t/won’t exist, they don’t have any interests that would give you a reason to believe that another outcome is better on their account (they have no account!). So, ignoring other reasons, this outcome is not dominated by any other, and the welfare of an individual whom we could bring into existence is not in itself a reason to bring them into existence. This is reflected by the absence of arrows starting from the Nonexistence block in the image above.
2. An existing individual (or an individual who will exist) has interests. In an outcome in which they have a bad life, an outcome in which they didn’t exist would have been better for them from the point of view of the outcome in which they do exist with a bad life, so an outcome with a bad life is dominated by one in which they don’t exist, ignoring other reasons. Choosing an outcome which is dominated this way is worse than choosing an outcome that dominates it. So, that an individual would have negative welfare is a reason to prevent them from coming into existence. This is reflected by the arrow from Negative existence to Nonexistence in the image above.
3. If the individual would have had a good life, we could say that this would be better than their nonexistence and dominates it (ignoring other reasons), but this only applies from outcomes in which they exist and have a good life. If they never existed, because of 1, it would not be dominated from that outcome (ignoring other reasons).
Together, 1 and 2 are the procreation asymmetry (reversing the order of the two claims from McMahan’s formulation).
I think my argument builds off the following from “The value of existence” by Gustaf Arrhenius and Wlodek Rabinowicz (2016):
Consequently, even if it is better for p to exist than not to exist, assuming she has a life worth living, it doesn’t follow that it would have been worse for p if she did not exist, since one of the relata, p, would then have been absent. What does follow is only that non-existence is worse for her than existence (since ‘worse’ is just the converse of ‘better’), but not that it would have been worse if she didn’t exist.
The footnote that expands on this:
Rabinowicz suggested this argument already back in 2000 in personal conversation with Arrhenius, Broome, Bykvist, and Erik Carlson at a workshop in Leipzig; and he has briefly presented it in Rabinowicz (2003), fn. 29, and in more detail in Rabinowicz (2009a), fn. 2. For a similar argument, see Arrhenius (1999), p. 158, who suggests that an affirmative answer to the existential question “only involves a claim that if a person exists, then she can compare the value of her life to her non-existence. A person that will never exist cannot, of course, compare “her” non-existence with her existence. Consequently, one can claim that it is better … for a person to exist … than … not to exist without implying any absurdities.” Cf. also Holtug (2001), p. 374f. In fact, even though he accepted the negative answer to the existential question (and instead went for the view that it can be good but not better for a person to exist than not to exist), Parfit (1984) came very close to making the same point as we are making when he observed that there is nothing problematic in the claim that one can benefit a person by causing her to exist: “In judging that some person’s life is worth living, or better than nothing, we need not be implying that it would have been worse for this person if he had never existed. --- Since this person does exist, we can refer to this person when describing the alternative [i.e. the world in which she wouldn’t have existed]. We know who it is who, in this possible alternative, would never have existed” (pp. 487-8, emphasis in original; cf. fn. 9 above). See also Holtug (2001), Bykvist (2007) and Johansson (2010).
You could equally apply this argument to individual experiences, for an asymmetry between suffering and pleasure, as long as whenever an individual suffers, they have an interest in not suffering, and it’s not the case that each individual, at every moment, has an interest in more pleasure, even if they don’t know it or want it.
Something only matters if it matters (or will matter) to someone, and an absence of pleasure doesn’t necessarily matter to someone who isn’t experiencing pleasure* and certainly doesn’t matter to someone who does not and will not exist, and so we have no inherent reason to promote pleasure. On the other hand, there’s no suffering unless someone is experiencing it, and according to some definitions of suffering, it necessarily matters to the sufferer.
* for example, when concentrating in a flow state, while asleep, when content.
See also tranquilism and this post I wrote.
And we can turn this into a wide person-affecting view to solve the Nonidentity problem by claiming that identity doesn’t matter. To make the above argument fit better with this, we can rephrase it slightly to refer to “extra individuals” or “no extra individuals” rather than any specific individuals who will or won’t exist. Frick makes a separate general claim that if exactly one of two normative standards (e.g. people, with interests) will exist, and they are standards of the same kind (e.g. the extent to which people’s interests are satisfied can be compared), then it’s better for the one which will be better satisfied to apply (e.g. the better off person should come to exist).
On the other hand, a narrow view might still allow us to say that it’s worse to bring a worse off individual into existence with a bad life than a better off one, if our reasons against bringing an individual into existence with a bad life are stronger the worse off they would be, a claim I’d expect to be widely accepted. If we apply the view to individual experiences or person-moments, the result seems to be a negative axiology, in which only the negative matters, on, and with hedonism, only suffering would matter. Whether or not this follows can depend on how the procreation asymmetry is captured, and there are systems in which it would not follow, e.g. the narrow asymmetric views here, although these reject the independence of irrelevant alternatives.
Under standard order assumptions which include the independence of irrelevant alternatives and completeness, the procreation asymmetry does imply a negative axiology.