I don't think I've ever seen you give any explicit arguments as to why birthrates are the end-all-be-all of cultural supremacy.
Why can't lower birthrates be balanced out by citizens who are longer-lived, richer, and more productive? Isn't it the case that one hundred thousand American kids who go on to have successful careers in science, business, the arts, etc., are worth more to a culture than a million ill-educated, ill-nourished, pissed-off would-be suicide bombers?
Reihan responds in full Brooksian splendor:
Why not sacrifice quantity for quality? Consider rapid economic development in Korea and China and elsewhere. Economic takeoff was preceded by steep declines in birthrates. And as industrial economies supplanted economies that centered on home production, childen became less of an economic asset and more of an economic burden. . . . That the birthrate has declined pretty consistently from the 1820s to the present in North America - leaving aside a few cultural blips, and even the Baby Boom can be largely attributed to the increased propensity of Roman Catholic families to rear four or more children - is thus not surprising in the least.
So what gives? Why do I think that this is a bad thing? . . .
Look at it this way - what are the qualities one needs to raise young children? Tolerance, kindness, forebearance - patience is one way of putting it. Having a decent regard for others is another. . . .
When I think about all of the things I consider most coarsening and tragic about contemporary life, I think they can be traced to this basic failure of empathy. I extend this to our indifference to extreme deprivation in the most benighted corners of the globe, and also to the breakdown of civility in neighborhoods, not to mention the dissolution of families.
Very sincerely, I don't think of myself as a particularly patient or thoughtful person. Consumption is the organizing principle of my life, or at least it's a close second to friendship and learning cool stuff (tied). . . . I figure there's probably a better way to live, not for me necessarily (and not for you necessarily) but for a community or a culture. . . .
I detect sadness - and I mean the deep sadness of very successful, very sharp, appealing middle-class North Americans in their mid-twenties, possibly the most privileged creatures to ever walk the earth in large numbers - it's about drift, basic mistrust, loneliness.
There's more to Reihan's response, which is deals with the X's and O's of why population growth is necessary, but this wonderful little bit of humanism ought to be appreciated on its own.