Do you want to have kids when you're older?

So for one I was half joking.

But let's defend this anyways.

Your first argument is a false dichotomy; basically implying that I either have to say a child's consent does matter or it doesn't matter, and that there is no in-between. If you really do believe that this is the case, then it leads you down some incredibly dark roads. There once was another person on the internet who made this argument, that person being Amos Yee. Amos Yee also believed that children could not give informed consent to anything, and thus their consent was not a factor to be considered. However, where you and Amos differ is that Amos was arguing for the removal of age of consent laws, meaning children could vote, smoke, have sex with adults, and sign long term contracts. If we accept the idea that a child's consent does not matter to any capacity, then Amos Yee is the logical conclusion of it, and I don't think either of us are comfortable with that. I wasn't saying that a child's consent doesn't matter in any capacity, I'm saying a child's consent matters less than a full-grown adult, because they're not mature enough to make their own decisions on certain things yet. Something that doesn't exist has exactly zero maturity and as such has no capacity for consent. We shouldn't take consent into account when the thing doesn't exist.
Even with this said, I believe that your framing of the argument is incorrect. I'm talking about the consent of the theoretical person in their entirety, not just in their childhood. The reason I'm pro choice but not pro life is because the life of a minimally conscious organism does not in any way concern me. That said, the life of a theoretical adult who could one day grow up to be resentful of the fact that they are alive DOES concern me. If you think that's unfair, think of the way we talk about climate change. The reason that I and many others care about climate change is because we want a secure future for the generations to come AFTER our time. I am not going to give the same consideration to a fetus that I would to a theoretical fully grown adult. You're absolutely right, the pro-life analogy was wrong. My bad.
Your argument that life is generally good for most people is also relative. All that the positivity offset does is make people perceive neutral situations as being mildly positive. Even looking past the fact that "neutral" is an incredibly loaded term that's relative to individuals, what if someone's environment means that the situations they are in aren't neutral? If I'm born into a slum it's likely that most of my life will be sub-neutral. I don't disagree. I do think it's immoral to have kids if you live in a hellhole because you'd be making them suffer. If you don't live in a hellhole, however, then it's fine to have kids because the chances of them living a horrible life are very slim.
Even then, I recognize that being alive is generally not bad for most people. But that doesn't make it moral. I firmly believe that circumcision is immoral, but the amount of people who suffer in a tangible way due to circumcision is probably low. The same could be said for other violations of consent; for example, if I were to give a baby a piercing, it's likely that they would not suffer adverse effects because of it. So should we allow piercings in babies? Let's get more abstract; let's pretend that there is a machine that you can be put into. The machine has a 99% chance of fulfilling all of your hopes and dreams, while it has a 1% chance of cutting off your arm. Now, if you forced ten people into the machine, the results are most likely to be positive. However, we wouldn't say that it was moral to force those people to use the machine, because there was a huge inherent risk involved with it. Their consent is what matters in that situation. The same can be said for living; even if your life is likely to be good, the truth is that there's always a chance you will experience immense suffering because of it, and your inability to consent to it is what's important. 
This is a bit of a false analogy. As for your machine, I realize this sounds insane, but if you somehow had a way to do that without them realizing, without anyone else realizing, and without anyone realizing afterward, and without humanity suddenly realizing that something is up since 1% of people got their arms suddenly cut off, etc, then yes, it would be fine to put them through it, but it's obviously impossible to meet all these conditions. The reason I have these conditions at all is that if everyone becomes suddenly paranoid that they will be next, then that's not exactly making people happy. If people realized what was happening to the 1% then there would be massive riots, and that's not exactly making people happy either. If this set a precedent that doing this type of stuff was okay and some people realized there was now a precedent then there would also be massive riots. Also, the 1% of people without arms would be significantly impaired, and who even knows what nightmares that could cause if it hit important people. You get the point. It's impossible to avoid all these conditions, so under all practical circumstances, I would not think it's ok, but if you magically managed to do ALL of this, plus make sure that no other awful side-effects happen that I haven't thought of (which is also near-impossible), then I would think it's ok. I understand you might not be comfortable with this either so in that case we'll just have to agree to disagree on that part on the basis of different morals.
Now, what you may be saying is that producing life is for the greater good; in that, it produces the most happiness for the most amount of people. And, if you believe that to be true, I can't call you incorrect. I can, however, point out how dangerous your ideology becomes. You've effectively embraced utilitarianism if you believe that the greater good is all that's important. My abstract example from earlier would be your model society; it would be moral to force all 7 billion humans through that machine because the net happiness would be increased as a result, even if 70 million humans had to lose arms as a result. And while that's bad, it's not even close to the darkest result of utilitarianism. Just to provide one example, if you were a genetic match for 5 people who needed organ donations (all of them needing different organs, of course), then it would not only be OK, but in fact morally correct to kill you and forcibly remove your organs in order to save those 5 people. Obviously that's not comparable to what you're suggesting, but it still shows the inherent flaw with judging an action's morality based only on its outcomes. This is also a false analogy. If someone went up to me, shot me, and stole my organs, then that would not by any stretch of the imagination on average increase people's happiness. I would feel pain from the shot, my family and friends would be devastated, people in my city would become paranoid that there's a creepy guy stealing people's organs, and the 5 people that received the organs might be happier than if they had died but they'd also be forever guilty. If you somehow magically avoided all this, then people would start realizing that random people are disappearing and then become paranoid. There's no way that you can, in real life, ever possibly avoid all these, especially considering my family would notice my disappearance no matter what (unless you also magically, painlessly kill them and everyone related to or friends with them and everyone related to or friends with... etc, in which case you'd probably collapse parts of civilization by how many people you kill). But, if somehow, in the situation that you managed to avoid ALL of this, which we already established is physically impossible, then yes, it would be morally correct.