Gregg points out the difficulty with low birth rates is that a country ends up with about two people working for each retiree. Those two workers must make contributions and/or tax payments sufficient to support that retiree's old age benefits - benefits that in the U.S. we call Social Security and Medicare.
From whence come the low birth rates? Birth control and women's liberation are the proximate causes; countries without one or both still have high birth rates. It is interesting how human rights improvements have unintended consequences.
