Exactly. Any object can be used as a weapon by the wrong person.
What's important is their intent: somebody who wants to do damage will, regardless of the restrictions on what
they can carry on a plane.

I think what El-Al does (individual interviews with passengers and a second party observing their responses [1]) is the most
security-effective way to do things, but ideally in a free world, such measures wouldn't be necessary at all.

[1] http://en.wikipedia.org/wiki/El_Al#Airport_security_measures