Oh for G-d's sake -- no one is going to try to hijack a plane with a 2.5" knife. Yeah, the 9/11 hijackers had box cutters. They also had mace and FAKE BOMBS, both of which are still prohibited. And they didn't have 100 other passengers ready to emasculate them if they tried to hijack. Nor reinforced cockpit doors. Nor pilots armed with revolvers.