Some restrictionists have made arguments that relate the problems of terrorism (such as the 9/11 terrorist attacks in 2001) with illegal immigration in the United States. There are some legitimate concerns about terrorism and immigration (as well as tourist visas) on the whole. But illegal immigration along the southern US border is not a contributor to terrorism. Some of the reasons are outlined below.
- Empirically, the case is simply false. Foreigners who’ve carried out terrorist attacks have entered the United States legally on immigrant, non-immigrant work/study, or tourist visas. While some of them may have been “illegal” in the sense of overstaying their visas, this is a qualitatively different problem than border crossing.
- Getting a tourist visa remains considerably easier than getting an immigrant or work/study visa. This point was made by David Friedman in a blog post titled Immigration and Terrorism.
- In recent history, most terrorism in the United States has been motivated by certain Islamist ideologies. Most illegal immigrants who cross the border to the United States come from Mexico and Latin America, where Catholicism is the main religion. Radical Islam has, if anything, less of a stronghold in these countries than in the United States.
- Apprehension rates for people attempting to cross the southern US border are quite high — about 25-50%. While this apprehension rate may be acceptable for drug mules and economic migrants who are desperate to improve their condition, it is not acceptable for people who wish to plan terrorist attacks, because they would get detained and fingerprinted and their network may get infiltrated. This point was made by Jeremy Shapiro, a national security expert at the Brookings Institution.
Open borders advocates have argued that an open borders regime would actually contribute to security by focusing the resources of law enforcement on criminal and terrorist figures. See for example the Open Borders blog post Secure the US-Mexico border: open it by John Lee (February 25, 2013).