You do know better than to try and carry nail-clippers in your hand-luggage, don’t you…?
If you were someone possessed of the sort of Mad Ninja Skills that would enable you, mid flight, to get up from your economy seat and shout, “This is a hijack! Take me to Jamaica!” while menacing crew and passengers with nothing more lethal-seeming than a nail-clipper, I’m guessing you probably know enough other ways to intimidate people and generally present a clear and present hazard to civil aviation than finding yourself in need of actual nail-clippers.
In fact, I’m more inclined to wonder how you managed to get onto the plane in the first place without being detained as a walking Weapon of Mass Distraction. I guess that as long as your passport doesn’t have your name as something like ‘al Rashid’ or anything else vaguely middle-Eastern, you’re okay to board. But I digress…
So the whole nail-clipper thing makes no sense whatever.
On the contrary, imagine that some underpants bomber is on a flight where ordinary passengers were legally permitted to carry nail-clippers. When the time comes and our imaginary bomber carries out his brief, the other passengers could simply nip his dastardly plan in the bud by snipping the wires of his bomb with their nail clippers.
See? It makes more sense to encourage people to carry nail clippers in their hand luggage than to forbid it.