Open Borders, in the article, "Terrorism and Illegal Immigration in the United States" (accessed Mar. 14, 2016), available on the Open Borders website, stated:

“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…

  • 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…
  • 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.”
Mar. 14, 2016