Because it's demonstrably successful at curbing population growth rate? Because during periods of the most aggressive enforcement of the one-child policy, China had its highest growth rate in recent history, 2-2.5x that of the US?

And now, during its period of least aggressive enforcement, but with a rapid pace of industrialization and wealth injection, the growth rate has fallen dramatically?

http://www.indexmundi.com/g/g.aspx?v=24&c=ja&l=en

Or perhaps we want to look at Japan, which without forced abortions, property confiscation, and brutal acts of repression have managed to achieve a negative growth rate?

No matter which way you slice the data, the trend is clear: industrialization, wealth, and stability decrease growth rates, and do so far better than any number of guns and Bibles you can point at people.