More important, though, the London bomb plot failed because open Western societies are more resilient than we sometimes think they are. One of the Piccadilly car bombs was discovered because an ambulance crew, responding to an unrelated call, saw smoke seeping from a car trunk and alerted the police. The other car was illegally parked, and London's super-vigilant, much-hated traffic wardens towed it to a parking lot, where someone noticed that it smelled of gasoline and alerted the police. That Britain has functional ambulance services and working traffic wardens, all of whom are civic-minded enough to call the police when...