Sabl also gives an explanation for the obsession over population growth differences, which unlike my handful of speculations, isn't quite so cynical:
To measure a country's well being by its growth in population is a VERY old habit; ancient historians did it, and the Enlightenment made a fetish of it. Perhaps it even made sense when a country could only survive through producing young men for war and when low population tended to come from pestilence and famine. But I think it's a habit we should drop. Leisure, culture, and independence are normal goods. As countries prosper, their inhabitants produce more of them—and, on aggregate, fewer kids.I think the historical explanation does have something going for it. It is only very recently that populations began their strong upward trend. Prior to about the 1600s in Europe, and much later elsewhere, populations grew very slowly if at all. Focusing on growth rates made some measure of sense, because individual tribes really did face the threat of going extinct, and for those who were able to grow, it meant they were able to successfully utilize the meager agricultural surplus available at the time. These days, however, population growth is more often a sign of poverty and other negative social conditions than of success. Whatever the case, we in the developed world aren't dealing with a meager agricultural surplus anymore. It's time we dropped the birth rate fetish.