Max, you clearly don't get the point that people are making.
If you allow passengers to have penknives, then you are allowing potential hijackers to have penknives. If you allow passengers to have hypodermics, you are allowing potential hijackers to have hypodermics. etc. etc.
If you allow any passengers to have a potential weapon that could be used to overpower a hijacker, you are allowing hijackers a potential weapon that could be used to overpower aircrew.
That having been said, as has already been pointed out, almost anything could be used as a weapon - a pen, a bunch of keys, a rolled-up newspaper with a few coins, etc. etc.
It is the height of stupidity to say that passengers should be allowed to carry these in order to attack hijackers. You either allow them to have them because they are lawful items to have in your possession, or you disallow them all and, as has been suggested, we admit that the terrorists have won this battle. But you do not "arm" (or allow to go "armed") passengers because they can overpower hijackers. That's the straight-line assumption of the gun lobby in the USA that says that criminals are armed, so everyone should be armed. There is no end to the madnes in that direction. That way there'll be an aircraft downed by breakup following explosive decompression within a year.
My personal opinion (for what it's worth) is that passengers should be allowed to have nail scissors, penknives, etc. since that is a normal item of hand baggage. Anything out of the ordinary such as stanley knives, screwdrivers, chisels, etc. shold either have to check them in hold baggage of have them confiscated.
As for overpowering hijackers, let's have no more talk of passengers being "armed". Whatever you think they might be able to take on board, you can assume they've got more of and more deadly than you happen to have mixed up with your toothbrush and make-up. The best weapon after Sept. 11th. is the will to live and overwhelming numbers.