I've also wondered about that.... what's the point of
having thousands of agents at airports and US/Canada
land-crossing points?

That's not going to stop the real terrorists.

Heck, Osama himself could lead a batallion of terriorists
into the USA undetected. He just has to use the half-mile
tunnel under the US/Mexico border that was found
several days ago.

I believe the agents sitting in airport immigration booths
should absolutely check everyone's document as much
as necessay. However, what's the harming of having a
smiling face and saying a simple "Welcome to the USA" ???