The American Middle Class is not populating fast enough; that is to say we have an aging population, but we are not having enough kids to support and run our nation and insure proper capacity, output and productivity to continue to grow our GDP at this rate, but we are not alone.
Japan also as a very old average population and it is getting up there and this has indeed affected their economy. Europe is next with its aging population, but it is importing Eastern Europeans and Muslims to fill the gap who are indeed having many children. In the United States we will be right behind Europe with our aging populations too and we need to produce more babies to take care of us in our old age and continue the GDP growth.
But for how long; well, forever or until there are so many people on the planet we have to start over as we cannot feed them all? Well that is a problem indeed; consider this if you will. You have some feces in a bowl and flies come and lay eggs and the larva eat up all of it and there is no more?
The larva cannot fly away yet but need food, what happens then? Ah ha, now you see the real problem with this theory, as exponential growth has its problems too. Nevertheless in the short term economists and bankers say that we must; Re-Populate US with Mexicans to Guarantee GDP Economic Growth. Oh really, and that is your plan is it? Consider this in 2006.