I flew on a plane without going through security. It was amazing and no one died.: The best literature review available on the efficacy of counterterrorism tactics found that, on average, adding metal detectors and security screenings at airports led to about 6.3 fewer airplane hijackings in the years examined (a hijinking-heavy period chronicled in Brendan Koerner's latest book, in case you're interested). But that was more than compensated for by an increase in "miscellaneous bombings, armed attacks, hostage taking, and events which included death or wounded individuals (as opposed to non-casualty incidents) in both the short and long run." In fact, metal detectors and security screenings at airports led to about 6.8 more of these substitute events. "When calculating the overall weighted mean effect size for all of the findings examining the effectiveness of metal detectors, the positive and harmful effects cancel each other out," the review's authors conclude.
Could that literature review be wrong? Sure.