Honestly, the biggest thing as far as I'm concerned is basic categorical imperative/collective action stuff. Unless you think expediting human extinction is a good thing,
someone has to have children. Not doing it isn't a universalizable behavior. It doesn't mean every single adult in existence has to procreate, but the baseline expectation if we want humanity to survive is that most do. Thinking of it in terms of personal benefit is the wrong way to look at it.
For what it's worth, I'm in my 40s and don't have children and likely never will, though I do hope to adopt. In my case, I'm a man, can't have children because of that, and my wife didn't want to for various reasons. It's ultimately up to her, and I'd rather adopt than divorce her. Is that a good enough reason? I don't know. But I don't personally see anything about the world and it's future making it bad enough that future human existence isn't worth it. I plan to continue existing as long as I can, and if I could exist long into the future, I would. If it's good enough for me, it's good enough for new humans, too.
Also, my wife has ADHD, and as far as I can tell, her existence is still worthwhile. Not bringing people into the world because you fear they'll develop ADHD doesn't seem like a good enough reason to me. If you expect to pass on some congenital condition likely to result in a short life of nonstop suffering, sure, forego that. But I don't feel like the common diseases of affluence, i.e. anxiety, attention span disorders, obesity, make life not worth living. Humanity has some work to do in order to figure out how to reconcile our evolutionary history and learned behaviors and mental proclivities with a dramatically changed modern world, but we should actually do that work, not give up and end the human experiment.