We all know that airport security and border security failed before 9/11.
What failed on 9/11 was the traditional policy of airline crew and passengers meekly submitting to the demands of hijackers. By 9/12 that policy was corrected, with no government intervention necessary.
Letting multiple armed men most of whom had passport and visa violations into airplanes was a colossal intelligence failure.
Letting "armed" men (with small knives) onto airplanes was not a failure of anything. There is no reasonable way to discriminate at boarding time between homicidal maniacs (an infinitesimal minority) and ordinary people. Trying to make that determination is unreasonable, as is preventing everybody from carrying anything that could possibly be used as a weapon.
Having a passport or visa violation does not make one a deadly threat. Plenty of harmless people with visa irregularities have managed to squeak past the TSA with no repeat of 9/11. A giant state security apparatus to ensure that everybody has all their papers and documents in order before they can travel ... that hurts far more than it helps.