OP you're pretty much gettin crucified so I thought I'd jump in with a more mixed opinion.
I don't really agree with your idea that you can't get consent from a non-existent person for them to agree to exist. If consent isn't a possibility, then that responsibility falls to you, if it's your decision whether or not they exist. Kind of like how some kinds of sick people are given power of attorney over their relatives to make decisions in their best interest. So I'm not with you on that.
Then you've got to think about whether it's a good idea to have a kid. So there are two things. There's the pessimistic view that in any given human life, there's more of a guarantee of pain than there is of happiness. I think you can make a good argument for that when you consider all the emotional pain and mental pain that comes along with a human life, and the almost guarantee that it will also end badly as well. On the side of happiness, you could argue that most of the time we aren't actively happy the same way pain is active, we just enjoy the absence of pain and spend our lives working towards keeping it at absent as possible. There will be counterarguments to that but I think it's an idea that holds a bit more weight than your consent idea.
On top of that, there are more than enough people in the world as it is, and there's no reason to assume that your kid will be of any net benefit to society. They might even be a drain. Resources are unevenly distributed and human impact on the planet seems to be pretty harmful overall, so even if you don't agree with the idea there should be less people, I can't think of a good argument why there should be more right now. So there are humanitarian and environmental reasons you could argue in objection to having children.
If you take the biological imperative to procreate out of it, it's a pretty simple proposition to me. I don't think everybody in the world should decide not to have kids, I don't think humanity should let itself die off, but I've got no issue with somebody who decides not to have kids for the two reasons I just mentioned.
Then there are some things in defense of it.
In relation to the pain/happiness judgment - if the desirable quality is happiness here, and having a kid will bring you great happiness, then in the absence of any other existing person (ie the kid), your happiness takes priority. So if having a kid makes you happy, you should do it, if that's all there is to it. It isn't all there is to it though, so you've got to think about whether the kid will be happy, and whether they are likely to cause happiness in the course of their life. Those two things will be your responsibility to ensure up to a certain point, so it's a lot of responsibility to take on. It can't just be about you, you've got to think about the kid and how they should ideally turn out.
As far as overpopulation goes, there are judgments to be made there. If you have prepared to have a kid properly, you will have an approach to their education and socialisation that makes it more likely that they will become a net benefit to society and possibly even the planet overall, even taking into consideration overpopulation and the harm humanity causes to itself and to the environment. That's another responsibility you take on - to provide the best possible conditions to make that desirable outcome more likely.
I haven't really come to a conclusion on this, though. As for me, I don't know if I will have kids. Right now I can't take on those two major responsibilities, because I don't have the desire to in the first place. Even if I did have the desire to have a kid now, I shouldn't, because I couldn't justify it for the same reasons. It isn't enough to want to have kids, if you're really asking the question. It is selfish and carries a lot of risk with it.
There's a pretty convenient option that puts all of these issues to the side though, which is adoption of an unwanted baby or a child who is being left to languish in some way. If I do have kids, I think I'd be a lot more likely to go for that. Some people might say they want the kid to be their own, but I think that's a pretty indefensible reason to bring another person into the world with everything else considered. Most of humanity does it anyway!