Terrorists don't need to visit the US to carry out an attack on American assets or citizens. Witness the Nairobi embassy, or the Cole. If you're serious about this idea of deporting all foreigners as a security measure, you'd also have to ban overseas travel by Americans. And what all this would do to American exports doesn't bear thinking about. How long do you think the boss of Dubai Chevrolet would keep buying cars, if he wasn't able to visit his supplier? Think it through, for crying out loud.......
It certainly makes it a lot harder for them if they find themselves back in their own countries. There have been many attempted terrorist acts, including an Arab killing Robert Kennedy here in the US by an Arab living here in the US taking orders from Arafat. This isn't about the Iraqi army landing on our shores, they are being sent here as agents of destruction to work within the US to bring it down.