It surprises me how many people want to end immigration.
We have a model for how that would work - Japan. A moribund economy with an aging and shrinking population.
The correct model on immigration control is the USA from 1925 to 1965.
As far as Japan goes in the long term they will be fine because Japan will still be Japan. Eventually their age demographics will shift downwards and the cycle of prosperity wll begin again for them.