I said most people, not you. I apologize if I made it sound personally.

That's alright, thanks for clearing that up.

Hooooowever, your analysis boils down to basically "having someone to bring me a glass of water when I'm on my deathbed", which is an argument used A LOT for, yep, rationalizing children.

Rationalizing wouldn't invalidate the argument. Also, I object to your summary. Would you exchange your parents (considering a loving relationship) for someone who just "brings you a glass of water on your deathbed"? Exactly.

In your analysis, have you considered the alternative of spending resources on fun instead of child-rearing, and then committing suicide before dementia kicks in?

Yes actually, and it's certainly true there are a number of years in which I'll have less fun with multiplayer games. That is, until I can have more fun with multiplayer games playing with the children (just an example). If "fun" only equated to "endorphin-release", we'd have to go for heroin-drips anyways. Happiness has more components. You don't climb a mountain because every step of doing so is fun, in fact many of those steps can be quite painful. Yet doing so can make you happy. (This is a bit generic of an answer, but then your "you should go for fun instead" wasn't very child-specific.)

Of course, utility calculations change when there are less resources available. I don't lack any material comforts because of the kids. Another one of those your-mileage-may-vary points.

And of course, all those people whose children are not there just did it wrong.

Yes, or did it right but got hit with the wrong end of the probability stick.

First I'd contend that very few people are able to efficiently optimize for reaching their goals even in a cursory manner. I wouldn't bet on a typical person being able to solve a Rubik's cube in a day. Children are harder, and the time constraints are comparably steeper. Watch typical parents in a Pizza Hut sometime. Are these the sort of people you'd trust to solve actually hard problems? Didn't think so.

Second, there are many contexts in which "failure" mostly equates with "doing it wrong" (If you do a 100 yard dash but fail to reach the finish line, chances are that you didn't get randomly hit by a whale -- though that's possible -- but that you did something wrong.) For a less wacky example, freshman college students not eventually graduating.

BTW, how do you construct a child?

You supply the nature, and you supply the nurture. You can influence both, and significantly so. I'm not sure what level of detail you're asking for, and much depends on the specific circumstances. It's just like problem solving (well, because that's what it is).

(Since your kid isn't yet an all-powerful AI, little quirks resulting from the invariable errors you make may be acceptable. So what if your kid randomly yells "I'M A VAMPIRE", charging strangers? At least their little missteps won't accidentally destroy mankind. Instead, they'll lead to karma on /r/childfree! Could be worse. Could be a fire dragon!)