I am writing this after the younger Boston bomber has been taken into custody. The news also included a note that some would want to prevent immigration reform based on the immigration status of the bombers, which would appear to be of 10 years’ standing with nothing to suggest illegal entry.
There’s no way to guarantee that someone who immigrates to the United States is not going to do something that attacks the United States.
Remember that Timothy McVeigh was not an immigrant, and we have just observed the 18th anniversary of that attack. The Unabomber was not an immigrant; nor are numerous native-born Americans that still attack the United States.