The anti natalist argument sounds absurd. For it to hold any water, I'd try to at least make sense of the following:
1- You have to prove (or at least give a convincing argument) that existence itself is inherently cruel by default. This is is pretty difficult because the perception of the "real" world depends on each individual. I'd argue that existence is meaningless and that the world as it is doesn't give a fuck about us being alive. The fact that we are concious beings seems to be more of a random accident of the universe. It doesn't mean that life is a gift from the gods, but that doesn't make it a living hell either.
2- I need to see at least a majority of people in the entire world expressing repeatedly their desire of not having been born at all. I'm not seeing this massive amount of people, honestly. Besides, we really can't ask someone who hasn't been born yet if they wish to live or not. That doesn't make life itself bad by default.
3- The fact that so many people aren't happy doesn't mean that their lives are not worth living or that their problems are unfixable. Happiness is complicated to measure, and its definition varies from culture to culture. If a majority of people in the world is suffering, i'd try to find the cause and fix it to the best of our abilities. Stoping people from reproducing is... a solution to that, not gonna lie. But it's an absurd one. It's like trying to reduce divorces by banning marriage.
4- This is something more personal, but I believe that someone who struggles with suicidal ideation doesn't make them devoid of joy. Even if most of my life I've been miserable because of external (abuse and trauma) and internal factors (hormonal inbalance) I know my circumstance is more the exception than the norm. If some day I decide to end my life, I doubt I'd resent my own existence. And this is something that you can only begin to question only if you live and make the decision on your own terms. Not being born gives me no choice at all in that sense
5- Everything previous to existence is a mistery, and it's impossible to prove that not being born is somewhat better than being born.