At one of my earliest jobs (I must have been 19), I had a boss who was incredulous that I didn't drink alcohol and said that I would when I was 21 because it was "part of being an adult". I was pretty sure that making my own decisions rather than letting myself get pressured by others into what they assumed was best for me was a more important part of being an adult, and over a decade later I still don't drink.

Comments like the parent one (pun semi-intended) basically sound the same to me as what my boss had said to me that day. Assuming that your own experience is universal is a flawed way to view the world, even if your experience is relatively common. If there are exceptions, it's not going to be easy to see them if you have an assumption already about it being universal, and if the people in the majority are loud enough and annoying enough about it, those who aren't will be even more incentivized not to share their experiences with you; I'd argue that people who regret having kids will potentially be reluctant to publicly say so. Most importantly, doing something because of societal pressure rather than genuine desire is going to greatly reduce the chance that someone truly finds it fulfilling, and there's an emotional cost for children who are raised by parents who basically regret having them.

It's totally reasonable to say "I never truly understood how much I'd enjoy having kids until I did, and I suspect it's the same for a lot of other parents". There's no reason to go further than that unless you're pushing an idealogy rather than actually trying to say something you know is correct.

My problem with that problem is that, well, people who have kids definitionally know (better?) about having them. Like being able to experience a book in its original version vs a translation.

It's okay if you don't want to learn Spanish, but when people discuss the struggles and delights of reading Cien Años de Soledad they're not necessarily being arrogant, just stating their lived experience.