Bullsh!t.
That's the easiest and cheapest problem in the world to solve. You lay off your minimum-wage security-checkpoint people, you sell all the machinery, and you let people carry onto an aircraft whatever makes them feel safest. Presto! no more hijackings.
Other terrorist activities may or may not be harder to bring to a halt.
They are likely to be useless in serious social encounters (indeed, it is usually male passengers who end up subduing "air ragers," according to several reports published over the past two years), serve crappy food and tiny soft drinks and coffee (all of which can be brought aboard by passengers), and generally are a pain in the ass with an attitude.
I would replace the aforementioned typical cabin crew of six or eight with two or more uniformed and plaincloths security officers who are highly trained (including some with paramedical qualification), highly paid, mentally stable, and experienced in the use of the weapons they carry, namely expandable batons, tactical edged weapons, and sidearms loaded with cartridges which contain frangible bullets.
Said officers would oversee cabin cleaning and maintenance, the loading of supplies (which would not include food and beverages, BTW), and the loading of luggage.
The cockpit crew would enter its domain through its own hatch and be separated completely from the passenger compartment by a Level IIIa antiballistic bulkhead.
Communication between the cockpit and security officers would be by pushbuttons designated to inform the captain of emergencies, etc. in only a general way (e.g. "Medical emergency. Land plane now").
So much for threats, demands, screams, noise associated with throats being slashed, and other distractions. Cockpit crew members then would be limited to performing their only proper function, which is to fly the damned plane.
Add to this the requirement that at all times at least one officer would be inside the protection of a locked and "bullet-proof" enclosure, and voila,' no more highjackings.
The cost of these measures probably would be completely absorbed by the savings realized by causing the flight attendant to go the way of the do-do bird.
The rules of engagement were forever changed last Tuesday, and the foregoing measures would address the fact that terrorists should be assumed to have only mayhem and not political goals in their hearts and on their twisted minds........