Shh, don't speak too loudly or those unobservant, stupid terrorists may find the loophole you've discovered

This is yet another one of the reasons many of us characterize the current security setup as being "ineffective" on many levels. Yes, it (usually) stops guns and knives from getting through, and hopefully stops explosives ... but there are so many easy-to-improvise weapons available just on the other side of the checkpoint that it's almost as if they weren't there, or are trying to bail water with a sieve.