Every day Americans suffer new threats. Blown up power plants, contaminated water supplies, Anthrax in US Mail...it goes on and on. We know who pulled off the big one. They're dead but their comrads, friends, are still here. We let them in. We know who they are. They are not citizens, so they don't enjoy all the rights of a US citizen. Which means we can deport them, thereby reducing their threat to National Security.
The reason we have not done this can only be blamed on Political Correctness. I can see no other reason. If you have an enemy whom you can identify in your country and you are at war, you remove that enemy. To me Political Correctness is distroying our National Security.