This blog on The Economist website includes a good summary of the dilemma that occupies much of this thread's discussion.
"One of the cruellest aspects of this tragedy is the impossibility of preventing recurrences. Technical faults, once diagnosed, can be fixed. Operational shortcomings can be ironed out, if never perfected. But when a person in a position of trust decides to betray that privilege, no amount of forethought or red tape can negate the threat they pose. If it could, then the “position of trust” would have been nominal only."
Germanwings flight 9525: A human response to a human tragedy | The Economist