As early as 1993, FBI director-designate Louis Freeh described how his agency perceived a looming danger [from widespread availability of encryption] and predicted, "The country will be unable to protect itself against terrorism, violent crime, foreign threats, drug trafficking, espionage, kidnapping, and other grave crimes."
As a mental experiment, let's go along with FBI director Freeh and try to envisage what might have happened if those bombers [in 1993] had actually succeeded in toppling both towers of New York's World Trade Center, killing tens of thousands. Or imagine that nuclear or bio-plague terrorists someday devastate a city. Now picture the public reaction if the FBI ever managed to show real (or exaggerated) evidence that they were impeded in preventing the disaster by an inability to tap coded transmissions sent by the conspirators. They would follow this proof with a petition for new powers, to prevent the same thing from happening again.
Such requests might be refused nine times in a row, before finally being granted on the tenth occasion. The important point is that once the bureaucracy gets a new prerogative of surveillance, it is unlikely ever to give it up again. The effect is like a ratchet that will creep relentlessly toward one kind of transparency, the kind that is unidirectional. A one-way mirror, under which we are all watched by officials, from on high.