The long tradition of special open borders between Canada, the US and Mexico has a good deal to do with being on a contiguous land mass, with areas like Point Roberts - wonder what they think of this proposal - or Alaska, and with post-land-war good relations between the three countries. The idea was that we ARE special - that we're all free people, living in free states, so (like the interstate borders in the US) the international borders in this case have more to do with legal jurisdiction than Us and Them. It's about trust, and egalitarianism, and the common rights and needs of humanity.
It's also a notion that has perhaps gone out of style with the ushering in of the new geography-based idea of the Homeland and its capital-S Security, ala amnotsurly's comment some time back. We'll need a new name for it, though. Iron and bamboo are already taken - the Pine Tree Curtain? That's overly local, though. How about the Black Gold Curtain. That pretty neatly sums it up - handles both borders nicely, and elucidates one of the bigger motivating forces behind the scenes as well.
The most pathological result of the WTC/Pentagon destruction has been the wave of ultra-partisanship that has swept the culture. These days, the most important thing is what 'group' you belong to. Are you a good person, or a terrorist? Are you right-wing or left-wing? Blue/Red/purple, ownership/serf, pro- or anti-, whatever whatever whatever. Can't prove you're a true-blue obedient papered-and-chipped US citizen? Then we won't "let" you back into the country. Can't prove you are clever enough to get yourself a photo ID? Then we won't let you into the Federal Building. Ok, whatever.
The elusive nature of 'safety' as bandied about these days always entertains me. How do you know when you are safe? It's the same linguistic disjunct as calling this exercise in building a caste system the "war on terror". When is it won, or over, this war? How do you know? You can't know for sure - and that drives the control freaks insane, so they go for the next best thing: cataloging all the possible dangerous elements of the situation. If you know who everybody is, and where they are, and what they're doing, and can watch for 'abnormalities' you can pretend you are safer.
The beauty of the nature of the 'terrorist threat' is how it forces the frame of reference to individuals - if you can't pick your enemy out of the crowd based on clothes or obvious affiliation, then anyone could be the enemy. Pretty soon everyone is the enemy until proved otherwise, until they can show you they are a member of an approved group. It breaks all our (humans) defense mechanisms to not be able to rely on a category as a means of distinguishing who to trust. So people become hyper-obsessed with making sure your group affiliation to SOMETHING is known, because then they can comfortably go back to dealing with you in terms of the usual cognitive framework.