“Slumping Fertility Rates in Developing Countries Spark Labor Worries” (WSJ, March 20, 2014) because the world loves cheap southeast Asia labor to produce cheap goods. Others will see declines in Thailand and elsewhere are good news in the effort to feed, clothe and house the world’s billions.
The trick is to plan for the decline, which has happened in every country since the eighteenth century Industrial Revolution in Europe. Can a smaller working population support themselves and their children as well as the older (sometimes larger) generation before? (Though usually a decline in the death rate precedes birth rate declines by a generation.) Yes, if the families have the benefit of labor-saving devices in agriculture, transportation and production (not to mention better education and health). It has been done.
There are all sorts of theories why this works, but the simplest is that top-down (intentional) modernization really works from the bottom up, driven by individuals operating in a free market. The freer the market the faster the transition (especially with the information revolution stacked on top of industrial and agricultural ones).
The great theorists always seem surprised that women, often of their own accord, cut family size in anticipation of improving their standard of living, seen as the third stage of Demographic Transition. Only where politics or religion force larger families lags behind. But even there (think of Roman Catholic southern Europe and South America) families sizes fall as women take control of their own destinies.
Bankers and state planners may wring their hands, but the people are usually better off when they control their own destiny. None of us may really control our destiny, but we tend to make better decisions than those in ivory-covered towers and windowless bureaucracies.