Earlier quoted context omitted.
Not to mention the US, Japan, and most if Europe is already below the replacement rate. Without immigration we are a dying society suggesting we need even fewer kids is a great way to end up extinct. Reolistically, in the long term we need to support young parents with policies that promote having more kids or accept that 'the American way of life' is a dead end doomed to failure.
You state that as fact, but it seems highly unlikely. Please cite your source.
Global fertility rate is dropping so depending on other countries sending new immigrants is risky.
US below replament rate: http://www.usatoday.com/story/news/nation/2013/02/12/us-birt...
Note the chart, US has been below the replacement rate ~2.1 births per woman since 1975.
PS: It's a fairly well established trend across a wide range of cultures which might change over the long term as populations shrink. However, my point is not that it's currently an issue for us, just that discouraging births is probably a bad idea.