Lets correct a few things.
Starting with the fact we do not need a 30 year recession to lower the population of the US.
Minus immigration we were already losing population prior to 2008 because of low birth rates among US citizens.
If you subtract just illegal immigration we still had negative population growth in 2008.
I just want to point out that the US had one form or another of legal immigration for over 200 years and the country managed to survive and thrive. Various branches of my family immigrated to the US over a 150 year span starting in the late 1700s when one individual came over listed only as cargo. He was an indentured servant.
Why do people think we have to allow illegal immigration to survive as a nation?