Restricting immigration is a form of rationing. When a situation becomes too big for government planners to figure out how they will get the taxpayers to foot the bill, the leaders and others call for rationing and other forms of restricting freedom rather than looking for freed market solutions.
Christopher Freiman dismisses the argument that we cannot have open borders because of the welfare system. See
There’s No Such Thing as a Closed-Borders Libertarian
Paraphrased excerpts:
[You’ll hear people make statements like: “I support open borders in principle, but we can’t have both free immigration and a welfare state so I reject open borders in practice.”
If preventing an increase in welfare justifies restricting freedom in immigration, then it also justifies restricting everything people may want to do.
Consider laws restricting people’s ability to consume drugs and sugary beverages, gamble their savings on professional sports, ride motorcycles without helmets. A major argument made on behalf of supporting these laws is that they prevent an increase in the consumption of state-provided benefits.]