Bruce Schneier explains what's really wrong about having the TSA screen for jars of liquid, knitting needles, and the like. His post begins with a TSA agent finding a jar of pasta sauce in Schneier's luggage. He confiscates it and tosses it into a bin full of similar jars of liquids. Schneier does not even bother to state the obvious: if those jars were explosive, tossing another explosive jar into the mix ought to be catastrophic; but no one thinks for a moment that there's the slightest danger.
Schneier moves on to a surprising conclusion. Check him out.