OK, suppose they did just that.
Just out of curiousity, how would you deal with the terrorist problem AFTER that? You'd have to have the government go on a hiring binge, get lots of people through security clearance requirements in record time, and get them familiar with their new jobs--and hope that the terrorists didn't take advantage of the chaos your idea would unleash...
The borders should have been sealed and every questionable character sent back to their home country.
Small problem--you just fired everyone in the INS and the Border Patrol, and a large chunk of the military as well. How do you seal the borders?
The FAA should have repealed their own law barring firearm possession on airplanes and let individual commercial lines set their own carry-on weapons policy.
And when a disciplined group of terrorists takes over another airplane with the guns your favorite airline would let them tote on board, and flies it into the Sears Tower...what would you do then?
BTW, if you say "Oh, but the people on the plane would pull out their guns, and shoot the terrorists," you're forgetting that firearms favor the few and the organized over the many and unorganized.
You're trying to argue with the same greate thinkers who said we shoulda had thirty thousand U.S. troops surrounding Tora Bora. (Never mind that this presupposed a build-up that couldn't of had them in place until months later.)