Well, because having a child, a descendant is so much more than “procreating”.

And, apart from that, your

“ I'm less interested in parents trying to rationalize what deep down they know was a bad decision, the perpetual "oh but I'd do it all over again" thing when clearly their life is a lot of worse and they're full of regret.”

is very judgmental.

One can be happy in the midst of hardship, difficulty and pain.

One does not have a child because “it is a benefit”. Unless one just sees life as a costly game.