Open borders are irrational in any free country. Known enemies of freedom must be denied entry, as do violent criminals and any other objective threats to the citizens of that country.
In a welfare-entitlement state such as America today, open borders become even more problematic. Particularly if new immigrants are put on these welfare programs at the time of entry. This puts productive and prosperous citizens in the position of economically supporting mass numbers of people against their will — the antithesis of freedom. In a truly free country, all charity is voluntary.
Libertarians and “Objectivists” arguing for open borders evade the solution they understand better than anyone: repeal the welfare-entitlement state. Phase it out in a defined time period. Even once this happens, you still cannot have open borders. But in an economically free society with no mandated obligations for welfare or “social insurance,” immigration would not be the huge problem it has become in our increasingly socialist society. The immigration policy of an America liberated from its welfare state will be: “Only self-responsible individuals need apply.”
Liberalized immigration isn’t tenable in a socialist society. Don’t blame it on racism or nationalism. Blame it on socialism.