So we're back to: you can't get consent for creating a new life. Since consent can't be obtained, you have to justify the position of doing something that affects someone without their consent.
There is precedence for this. I think a better analogy, that avoids the paradoxical issues of non-existence, would be life-saving treatment for someone who is unconscious. The treatment can either be administered (without consent, due to the patient being unconscious) to save their life. Or the treatment can be withheld and the patient dies. Justifying this treatment is predicated on the treatment being to the benefit of the recipient and is generally accepted with some various exceptions.
Many people would be of the opinion that creating a new person is beneficial to said new person. However this is where the fundamental disagreement between antinatalists and pronatalists would be. Is creating a new person beneficial or detrimental to the person being created? The hard antinatalism position says that it is "always bad", but of course the answer to this question can be conditional as well and need not be an absolute "always good" or "always bad". And people have different thresholds for where this point is. That's it, that's the difference of opinion.
/r/worldnews : yabbut it's not genocide because reasons