I am an antinatalist. There are lots of arguments for the thesis. But I think a very prominent argument for it - the most discussed in the literature - is bad: Benatar's argument.

In his book "Better Never to Have Been", David Benatar defends a supposed asymmetry between harm and benefit and appeals to this asymmetry in making his case for antinatalism (the view that we ought not procreate). But I think it's really bad - I think there are at least three problems with it: the asymmetry he posits has no explanatory value; the asymmetry he posits is incoherent; and finally the asymmetry implies procreation is bad if we do not pre-exist, but not bad if we do, whereas intuitively it should make no difference either way (that is, whether antinatalism is true or false, it should not turn crucially on whether we pre-exist or not - yet Benatar's argument makes it so).

Benatar's asymmetry

Benatar argues that absent harm is good, even when there is no one for whom it is good. By contrast, absent benefit, thinks Benatar, is not bad unless there is someone for whom it is a deprivation.
So, the asymmetry is that the goodness of absent pain does not need a subject - there does not need to be anyone for whom it is good. By contrast, the badness of absent benefit does require there to be a subject - a someone for whom its absence is an deprivation. Thus, absent pain is good, but absent pleasure is not bad.

That asymmetry is not self-evident to reason. That is, it is not intuitive in the way that, say, 2 + 3 = 5 is. As such it needs to be motivated in some way - we need some justification for thinking it is real.

Benatar recognizes this and motivates it by arguing that its reality is the best explanation of our rational intuitions about certain cases. For instance, imagine it is true that if Sue and Dave procreate, their offspring will have lives of total agony and then die. Well, it seems self-evident to reason that they ought not procreate. By contrast, imagine that if Mr and Mrs Bartricks breed, any child they have will be very happy. Well, it seems self-evident to reason that Mr and Mrs Batricks do no wrong if they refrain from procreating. So, it seems that we have a positive obligation not to create miserable lives, yet no positive obligation to create happy ones. Benatar takes this to be obvious - and i agree, it is - and says the asymmetry between benefit and harm explains it. For the absent suffering is good (and thus Sue and Dave do good by not procreating), whereas the absent happiness that Mr and Mrs Bartricks' decision not to procreate creates is not bad.

First problem

Our intuitions about the miserable life and happy life cases are asymmetrical and this is why they cry out for explanation. However, all Benatar does by way of explanation is appeal to a supposedly more general asymmetry which these intuitions reflect. How's that any kind of explanation? The asymmetry that Benatar is appealing to also cries out for explanation. Indeed, it is not really a distinct asymmetry - it is, by hypothesis, the same asymmetry, as our intuitions about the happy and miserable life cases are supposed simply to be reflective of it. So it doesn't really begin to be an explanation. It's akin to me asking "how does this watch work?" and receiving the answer "well, it is a particular instance of a watch from a company that makes working watches. Its watches work - it is known as the working-watch-company for a reason - and this is a watch". So, the first problem is that it is no explanation at all. You can't explain an asymmetry by just supposing it to be an instance of a more general asymmetry that itself requires explanation. (And Benatar can't deny that the asymmetry needs explaining - for if it didn't need explaining in the miserable and happy life cases, then his asymmetry is wholly unmotivated).

Second problem

The asymmetry he is proposing is incoherent. This is because absent harm cannot be good if there is no one for whom it is good. If a state of affairs is good, then it is morally valuable - that's true by definition. But something cannot be morally valuable if it is not valued. Where there is value, there needs to be a valuer. The idea that there can be moral value without any valuers seems every bit as confused as thinking that there can exist suffering without any sufferers. Thus, for anything to be morally valuable, there needs to be at least one person who is valuing its being as it is. And whatever it is, that state of affairs will then be good 'for' that person. Thus, there is no such asymmetry. Absent pain is indeed good, but it is always good for someone, just as pleasure is good when it is good for someone. In a world devoid of subjects, nothing would be good or bad. To put it another way, Benatar's asymmetry assumes the truth of some kind of moral objectivism about moral value, a view that is incoherent.

Third problem

If we pre-exist, then the asymmetry does not apply to procreative acts. So, Benatar's case for antinatalism only applies if procreative acts literally summon a person into existence. If instead procreative acts transfer an already existent person from elsewhere to here - which for all we know, they may well do - then it does not apply. Yet intuitively that should surely make no difference? Granted, if we had some reason to think that, 'if' people pre-exist, then they exist in a state of agony, or a state of great pleasure, then plausibly this would make a great difference to the morality of procreation. But in the absence of any reason to think that pre-existent life is better than, worse than, or the same as life here, then our pre-existence should make no difference to the morality of procreation - yet Benatar's argument implies otherwise. So much the worse for his argument, then.