This doesn't strike me as crazy. Appeals to nature are obviously not very good counterarguments. That the human race would go extinct if we all became persuaded of this also doesn't make it obviously wrong; if moral value is about actual individuals then it's plausibly not wrong for everyone to just decide to let humanity die out.
And in general we think it's a problem to subject people to stuff without their consent. In some cases we say that you simply can't do certain things without consent, and that even extends to cases where consent is not possible. We're most comfortable talking about consent when it comes to sex; you can't have sex with someone without their consent. Some people - minors and coma patients, for example - can't give consent, and so you just can't have sex with them.
This strikes me as something like the coma patient case - it's just not possible to ask a person to consent to be brought into existence, since you can't possibly get consent from them for anything until they begin to exist.
Now, I don't think that means it's always wrong to bring a person into existence, but I can see the argument. I think the response is that we don't think that consent is everything. If an unconscious person with multiple gunshot wounds is dropped off at the emergency room, the hospital is going to treat them even though they can't get consent, and even though in general we do think it's very important to get someone's consent before cutting into them. You don't have to have consent if you can't get consent and if you're doing a lot of good, especially if you're trying to help the person.
And so for me it just becomes a question of whether the child's life would be overall good. I don't think the question of consent is unimportant or totally misguided, but I think that at most it means that you shouldn't have a child unless you can provide it with a reasonably good life rather than a barely adequate one. Of course figuring out what constitutes a good or adequate life is itself not easy.