Schneier makes in interesting point that I’d overlooked about the problems with confiscating liquids, nail-clippers, etc.
I’d focused on the pointlessness of confiscating this stuff in the first place (water actually doesn’t explode; keeping small sharp objects out of passengers’ hands doesn’t prevent terrorists from using parts of the cabin for the same purpose, etc.) and therefore not even thought about the “but what if they actually are useful” question.
If a terrorist actually has some use for any of the routinely-confiscated (i.e. without provoking police involvement) items, (s)he can make any number of attempts to get one on to a plane. If the first nine attempts are thwarted by a confiscation, but the tenth attempt is not, then all of the airport security measures have not even been a serious hindrance. (Contrast what happens to you if you try to carry something which appears to be a bomb onto a plane.)
So many counter-productive ways to do security.