A Question on Airport Security

As I am flying tomorrow for the umpteenth time, I was wondering: Why won't they let me take my Swiss army knife on the plane?
The issue of air-security, as I understand, began to be high priority after 9-11. But then men who hijacked the planes were only successful in 3 of 4 attempts, as in the fourth attempt the passengers knew the aims of the hijackers. Most often hijackers want the vehicle to dock in a neutral area and then the hostage negotiation team is brought out to free the people aboard. These nuts however, decided to kamikaze into various important buildings. Hence, in the fourth hijacking, when the passengers knew the aims of their assailants, they did not comply. Assuming that, as Hobbes puts it, any man can kill another (with twine, a sharp pencil, etc), the question then becomes not whether or not we should allow box-cutters on planes, but what standard procedure should be for dealing with hijackers. Assuming As that appears to be the case, why can't I bring my Swiss army knife on a plane!