Immigration Policy
The problem is too little immigration, not too much.
The right way to reduce illegal immigration is to legalize immigration.
Immigrants presumably benefit from immigrating. That should count in evaluating immigration policy. It is arbitrary that some people or their ancestors were lucky enough to have already migrated to a better country.
Even if one does not value immigrants themselves, immigration helps the receiving country by increasing labor supply and promoting competition and innovation. Some native workers lose out, but that is the nature of competition.
A reasonable way to reduce immigration is to end the war on drugs, which creates much of the violence and dysfunction in Latin America.
Some legal scholars argue that the Constitution does not give Congress or the President authority to restrict immigration, except in narrow circumstances.
Immigration and naturalization (citizenship) are different. The Constitution does give Congress authority to regulate the latter.
All libertarians support major increases in legal immigration. Many endorse “free immigration,” under which virtually anyone can migrate. Some libertarians (including me) endorse literally open borders, similar to the U.S. system before World War I.
A possible negative of immigration is an increased burden on programs like SNAP, TANF, Medicaid, Medicare, and Social Security. The evidence, however, suggests that immigrants generate a net fiscal benefit, since immigrants pay taxes and contribute to a more productive economy.
Even if immigrants impose a fiscal burden, the right response is to limit eligibility for health and welfare programs to those who have resided in the United States for at least, say, ten years. Better yet, shrink or eliminate these programs.
Reasonable people can worry that opening the borders might have transition costs, e.g., overcrowded public schools. The right response is not to limit immigration but to move toward open borders at a moderate pace. Liberalized guest worker programs are one approach.