There seems a touch of playacting in the outrage that France, Germany and other European governments have been venting since the online edition of Der Spiegel, the German news magazine, reported last weekend that the National Security Agency had bugged diplomatic offices and monitored their internal computer systems.

Spying on allies looks bad and is rarely discussed in public except when, as now, spy agency documents are leaked to the press. But governments on both sides of the Atlantic (and almost everywhere else) have spied on allies and enemies alike for a long time.

We are far from the era when Secretary of State Henry Stimson, in explaining his decision in 1929 to close the State Department’s code-breaking office, said: “Gentlemen do not read each other’s mail.” The NSA was secretly created in 1952 with a mandate to intercept all kinds of communications from foreign sources, using every kind of listening device imaginable.

The new element is computer technology that makes storage so cheap and data analysis so fast that the agency now faces no technical constraints on how much data it can collect and use. That makes policy restraints all the more important. But it is hard to debate wise policy when every detail is kept secret from public view.