It’s not about individuals having children, but a society that collectively has few to no children. 9 out of 10 people age 45+, if they had to do it all again, would have had children: https://news.gallup.com/poll/164618/desire-children-norm.asp.... Only 1 in 10 wouldn’t have had kids if they had to do it over. Immortality would universalize the experience of the 10% to the other 90% of the population.

And? Having children isn't the sole determinant of our well being/happiness nor do they necessarily actually determine happiness.

Moreover, it's a reflection of current society, not a society of immortals. People for the most part considered immortality a foolish dream or actively hostile to the idea, driven by cultural inertia and active cultural reinforcement.

Lol...I'm pretty sure people would actually be happier.