David Friedman asks how we can trust TSA when it has shown itself untrustworthy. He gives two examples:
To take the earliest and most striking example, the TSA used to, for all I know still does, interpret the rule against knives to cover the inch long nail files sometimes built into nail clippers, with the result that anyone who happened to have a nail clipper with him and did not want to trash it was required to let them break off the file. To take a long continued example, the TSA insists that its agents be able to search our luggage but has failed to take the most elementary precaution to keep them from pilfering valuables--including in the note enclosed in searched luggage a number identifying the agent who searched it. In these ways and others, the organization has demonstrated that its concern, insofar as an organization can be said to have concerns, is with something other than the welfare of the people it claims to protect.
And, for the latest example, the TSA initially insisted that the new search requirements applied to pilots as well as passengers. Only after someone pointed out to them that a pilot who wanted to crash the plane he was flying didn't need explosives to do it--and, more important, after it became clear that enough pilots were unwilling to go along with the requirement to provide, at the least, a very serious public relations problem--did they reverse that part of their policy. The implication is either an organizational IQ at the idiot level or, more plausibly, an organization more concerned with image than substance.
And then there are the individual pieces of evidence on trust, such as this case where the TSA failed to follow its own rules and, this video alleges, punished a woman who wanted it to follow its rules: the TSA made her miss the flight.
I pointed out in a talk on C-SPAN in late 2001 that one should be skeptical of government running airline security when that same government still requires that flight attendants show you how to fasten a seat belt.