I used to think similarly but I disagree.

Within a given country you have a huge variance of fertility that as far as I can tell is completely predicted by religious affiliation and intensity thereof.

In my professional NYC suburb 3 kids is the norm (2x national average) and while nobody would describe themselves as religious everyone has some sort of affiliation (eg belong to a temple or church and go occasionally even if kn auto pilot). Meanwhile my tech and finance peers who are explicit atheists have roughly zero kids on average. And a few zipcodes down are more religious communities where the average is closer to 6.

So the three groups of people live in exactly the same country and area and experience themselves totally differently. I also frankly find that a lot of what is perceived as the reason people don't have kids (work, economy, cost, etc) is more a retroactive excuse because for everyone who has this excuse there's someone else living next door making the same salary who has kids.