The "they" in your last comment should reflect the reality that "anyone" coming into our nation is a potential facilitator of nuclear terrorism or worse. Let's face it, the right biological or viral release on US soil could wipe out a significant portion of our population. Yet our government couldn't seem to care less about our borders and who or who doesn't come across them.
I see 09/11 as a minor wake up call, not the seminal event that others do. And internalizing our efforts at security is pointless. Once the terrorist enters our nation, it's already too late. Who's to say that any one suicidal nut couldn't enter our nation infected with a mortal virus?
We need to clamp down on immigration tighter than a clam's arse. Will we do it? No. Why?
It does come down to open borders, for a lot of us. After 9/11 the military should have locked them down without question. Yes we're a free society, and we still can be without committing suicide. We MUST know who's coming in and out of the country as best we can, it's common sense.