Part of the Peter Principle (in a hierarchy a person rises to the level of his/her incompetence) states, "Competence is in the eye of the beholder."
To an airline passenger, a security officer obsessively concerned with catching parents of small children smuggling juice boxes or someone wearling glasses but having contact lenses in solution in a small plastic carrier is not competent. Why not check for suspicious electronic equipment? Why not sniff for gardenia scent? Why not look for sharpened plastic implements that won't show up on an x-ray?
Because the employee's competence is determined by what the higher-ups say, and what they say is to check everyone's shoes (despite the only previous attempt at exploding shoes being one dumb failure) and confiscate all liquids (despite the very questionable nature of the "exploding liquids" case in Britain).
