CONSIDER the purchase of a home in two adjacent gated communities. Both have houses with truly impregnable locks. In one community, whenever you need to enter your house, you visit the management office and show your driving licence. A guard walks you to your home, and lets you in using the master key that opens every door lock in the community. You can stay inside indefinitely. If an employee misuses the key to wander into homes or, heaven forfend, a thief gets his hands on it, all bets are off—the households' sanctity has been compromised.
In another community, the management requires that you privately choose your own lock and corresponding key, which you hang on to and use to enter your abode at will. But if you lose the key, or any copies you have made, you can never re-enter. It will remain a sealed edifice until the universe's heat death. Which would you choose? The latter offers extreme privacy but with an unthinkable penalty for carelessness. The former is convenient but there is the risk of the key falling into the wrong hands.