A suicide bomber set himself off at the Moscow airport in an area where people wait for arriving passengers, killing 35 and wounding 180. So now security experts are trying to figure out how to implement security measures at ticket counters, baggage claim areas, and the rest of the terminal that has public access.
Again we see the pattern: Airport security responds to a threat by imposing a security measure designed to make the attack physically impossible. Terrorists stop using that tactic but a adopt a new one. Airport security addresses that. Then terrorists try something else.
It would be nice if our security people would anticipate a threat, for once, instead of always reacting to the last one.
And even if we require going through metal detectors to get into the airports, a bomber could always blow up the people waiting in line. And if that were made impossible, he could kill even more people at a shopping mall or somewhere else. So to achieve total security we would have to put metal detectors and full-body scanners everywhere.