To start, Milton Friedman, a definite libertarian, did say this. That is the small truth that is too often delivered with a big lie.
This was not Milton Friedman's point, as anyone who has read his quote in context knows. But too many people maliciously take it out of context.
What that does is put stress on welfare programs.
What does stress do to things?
In Friedman's example, having open immigration puts stress on a welfare state.
More immigration, more stress.
Either the welfare state will reduce to adapt to the stress...or it will break.
They fight to keep the welfare state going as long as possible, by reducing the supply of new citizens.
Some also argue that immigrants are less valuable than natives.
Look at the retraction of European countries from the world economy and their collapse of dynamism that stem from their expansive welfare states.
They want an American that is weak, stagnant, and dying.
If you want to collapse our economy like Japan, put on that MAGA hat and support the wall.
If you want it to grow, support free trade in all markets, even labor.