Thanks for your hyperbole, it paints an extraordinarily realistic picture of the fundamentals of growth.

Our population has doubled since 1960, or over about 3 generations.  We fell below the replacement birth rate in the 70s, and 2/3 of our growth in recent years was from immigration.  The current rate of growth is quite low.

If you agree growth is good -- not all of us do -- it has to come from increased birth rates or immigration.  I favour the former, since investment in our own citizens makes more sense to me than investment in foreign nationals.

If you don't agree growth is good, immigration restriction will cause a significant drop in population.  My own feeling is that will come with a concomitant drop in standard of living and sustainability.