I saw this on Colbert & on 60 Minutes. He has an article on the same topic in The Atlantic. I see his point. It's all about impression management. Here's the deal. Say you were to bring aboard various contraband, particularly liquids. If you're "caught" with liquids/pastes, you just dump them. There's no analysis of the contents. There's no documentation or database of these transgressions. It's a matter of statistical probability. Sometimes sutuff gets through, sometimes not.
It reminds me of the "failsafe" velociraptor cage in Jurassic Park. Go to 33:41. I feel a dangerous game is being set up. Those wanting to breach security know that a tube of Colgate is treated no differently than disguised more deadly cargo. Additionally, getting stuff through security is just a matter of probability & if you're "caught" with contraband, typically, there's no penalty for it.
Is all of the screening just the benefit for us travelers? Jeffrey has shown that the security net is far from failsafe. Is the screening just marketing the idea that we're more safe or that measures are being taken that something is being done in our post 9/11 circumstance? If so, is it worth the costs?