Your making the same arguments as those for gun/knife/whatever control. Assuming me guilty until a pat down prooves me innocent does nothing to stop terrorists. Banning items does nothing to stop terrorists. Banning people like me who carry at least a leatherman that I would use as self defense if necessary does nothing to prevent planes from being taken over.
The next wave of terrorists will simply buy their operatives a gym membership instead of any banned weapons so they can overpower the defenseless sheep with their bare hands. The end result will still be the same except we will have wasted more tax money hiring people to steak SAK's and sell them on ebay.