This may be the unspoken, silent reason why illegal immigration to the US has been allowed to occur without too much resistance. Yeah, there are short term problems, but long run, you need a young working population to support the economy.

All the major Western countries, including Japan and China are aging. Even the underdeveloped countries will slow down in its birthrates eventually as well, as they grow more wealth and become educated. More and more of the population is not economically productive. The population becomes top heavy with the elderly. This is anathema to growth. Economies will eventually become stagnant. The thing you can hope for is that technology advances so dramatically that its effects on economic advancements will supplant the loss caused by aging.

People....have more babies!! The act to create one, I hear, is a very pleasant experience!