From the Barry Goldwater years on down through the Reagan era, conservatives have believed in limited government and individual liberty. Economists like Milton Friedman have argued the inefficiency of central economic planning. Regulating the flow of immigration into a country creates economic distortions, however, just like centrally planning the quantity of any other economic good.
If a bureaucrat in Washington cannot possibly have enough of the disparate economic information out there to make a sound decision about how much and what kind of health care insurance you should buy, how could it possibly have enough information to determine the "right" amount of immigration with a better result than the free market? And in the process, why should conservatives-- who believe in limited government-- want to expand federal policy into this issue faced by states, and why should conservatives want to expand state policy into an issue faced by individuals? What about the individual liberty of the immigrant family to travel and seek out better opportunities for itself as they arise? What about the individual liberty of the private company to hire an immigrant to work for it?
Many conservative talk radio personalities and pundits have expressed concern that increasing Latino immigration is balkanizing American culture, but it is doing the opposite. Conservatives have generally held strongly to a belief in the importance of families, traditional faith in God, and a hard work ethic. These are all prominent features of Latino culture as well. As for conservative fears of language balkanization, the entire history of immigration in the United States up until now strongly suggests that Spanish-speaking immigrants will learn and use English as new generations of their families take root in America. There should be no serious concern that a nation that hasn't yet adopted the metric system will ever have a foreign language foisted on its people against their will.
Conservatives should welcome as many immigrants as want to come to our country, because immigration is the ultimate act of entrepreneurship and risk-taking; it fills America with some of the boldest, most hard-working, opportunity-seeking, risk-taking, and interesting people from all over the world, strengthening our society and making our economy more robust. During the Bush years, conservative foreign policy centered on bringing democracy to the world, but by simply allowing the free flow of people across our borders, we can bring the people of the world to democracy, creating a haven of liberty for the world's disenfranchised to visit and join, and putting pressure on repressive foreign nations to change policies that drain them of their best talent as it emigrates to America.
There are many reasons why a conservative can get behind a more welcoming immigration policy.