SEOUL—A cultural preference for male children has cost Asia dearly. Count up all the girls who were never born because of selective abortion, victims of infanticide and females who died from neglect and there are upwards of 100 million women missing on the continent today by some estimates.

Not just a human-rights catastrophe, it is also a looming demographic disaster. With Asian birthrates already plummeting, that is tens of millions of women who will never be mothers. The economic and social impact on some of the world’s...