Those that pose a threat include psychos, criminals, asylum seeks and our old adversary, the terrorist. Criminals are generally after cash - it's easier to become a lawyer or a city trader (same people) and escape with the cash. So as far as aviation is concerned, they are not really a threat. Asylum seekers now find it difficult to get near aircraft - low threat level. Psychos are generally loners, so lack back-up - low threat level. Which leaves our religious wackos. Misguided but intelligent, resourceful and highly motivated vs the numpties who run security. Not a fair fight. Also, do you think for one minute they'll come through the front door? And remember, passengers now know what when these guys take over a plane, so they'll have to choose a different method or target. So selling a few Swiss Army knives (as long as the blade is not in excess of 6cm) won't change the price of bacon.
Eliminate the terrorists and/or eliminate their grievances. It's that or we'll be enduring the theatre of security for decades to come.