First of all, as stated in other texts, the basis of the moral position of antinatalism is not that life is necessarily unworthy, but that it is necessarily unworthy to create new life. And it is not necessarily unworthy to create a new life because life is necessarily unworthy, but because in every creation of life there is necessarily a risk that it will be unworthy.
Additional reasons are because new lives were necessarily created without the consent of those who would live them, because they were necessarily created not for the sake of those who would live them as after all they did not ask, want, or need to exist before they existed, and because every creation of life, even if worthy in itself, is necessarily involved in harming others and making at least part of the lives of others unworthy.
Second, if you think people should determine themselves whether their lives are worthy or not, why do you support the creation of life of other people? If from your point of view we determine that people’s lives are unworthy by opposing the creation of new lives (even though, as mentioned, this is not the reason behind our position), aren’t you determining for other people that their lives are worthy by supporting the creation of new lives? How is creating people not determining for others that their lives are worthy?
It is not us who purport to determine for other people that their lives are unworthy, but rather it is supporters of reproduction who not only claim the right to determine for others that their lives are worthy but even force others to live lives that may or may not be worthy in their own eyes, relying on their determination, and not the determination of the created people, that the life they produce will be worthy.
Because reproduction is seen as something so accepted and taken for granted people don’t think about it, but every decision to create someone is a determination for them that their life will be worthy. That is why it is precisely the supporters of reproduction who determine for others whether their lives are worthy.
And even if we really determined for others that their lives are unworthy, it would not be forcing anyone not to exist, since it is impossible to force anything on someone who does not exist. On the other hand, those who create new people do force other people to live lives that, at least in some cases, will be unworthy in the eyes of those who live them.
Thirdly, it is clear that people cannot determine whether their lives are worthy or not before their lives have begun (nor can they do so before their lives are over since a worthy life can become unworthy at any moment due to a multitude of factors and reasons), therefore, since it is impossible for people to determine whether their lives are worthy or not before it happened, according to the logic of this argument, people first of all have to be created and live their entire lives (since only at the end of life can assessments be made about it), and only then can they truly determine whether it was a worthy life or not. However, of course, as far as the creation of new people is concerned, this argument contradicts itself since, in order to determine whether it is appropriate to start a life, this life always has to start.
In addition, this argument has a cruel implication that even particularly devout pro-natalists are unlikely to accept. By the logic of this argument, it is never the case that life should not begin because it would be unworthy, including cases where it is known in advance that it would be very miserable even by the standards of devout pro-natalists. It is doubtful whether the proponents of the above claim would support such a cruel implication. If no external factor can determine whether a life is likely to be unworthy, there is no life that it is unworthy to begin, and almost no one thinks that. Even ardent pro-breeding advocates think that cases of identifying serious birth defects or diseases are lives that are better not to start. In other words, at least in some cases, behind this supposedly liberal claim that people should determine for themselves whether their lives are worthy or not, stands a compulsion to live miserable lives, including by the standards of devout pro-natalists, just so that whoever makes this determination would be the ones living them and no one else.
And in any case and most importantly, a life unworthy in the eyes of those who live it will inevitably be created. Even if it will be a small minority, still, because no one needs to be created, and because no one will be harmed if they are not created, it is morally wrong to create people considering that some will feel that their lives are not worthy.
You don’t have to presume that everyone’s life is unworthy, or that the lives of specific people are unworthy, or that actually no one’s life is unworthy, in order to hold anti-natalist positions. It is sufficient to know that the life of certain people would be unworthy in their eyes and that they would prefer not to have been created, in order to oppose reproduction. And the reason is that with every reproduction there is a chance of creating a life that is unworthy, not in our eyes but in the eyes of those who will live it. Since it is impossible to know in advance which cases of reproduction will create an unworthy life, or if and when a life will become unworthy in the eyes of those who live it, all cases of reproduction are morally wrong. We do not have to determine for people that their lives are unworthy, but only to know that unworthy lives in the eyes of those who live them are always a possibility, and that it is never a possibility that those who were never created will somehow be harmed by it. These two premises are sufficient to establish an anti-natalist claim without any need to determine for anyone that their lives are not worthy.
The fact that no one is harmed by a worthy life that no one lives, but everyone who lives an unworthy life in her/his own eyes is greatly harmed by it, is more than enough.