My area of research when I worked at NASA was on the psychological aspects of space flight. I was involved in astronaut selection and in identifying the psychological stressors of space and developing countermeasures against them for operational use. One of the issues connected to this research used to bother me a lot and it was this: preventing something from happening is a good thing (e.g., you obviously don't want astronauts manning a space station or on a 2+ year trip to Mars to become suicidally depressed and become a risk for the mission), but by the very act of preventing such a thing from occurring you can never then prove that it might have occurred in the first place. Critics can then claim that the countermeasure/preventive action was not really necessary to begin with. The same is true of selection techniques--or in fact, of almost any preventive measure in any area. If you are successful, the event you fear will not happen. So, were you wrong to try to prevent it?
John Podhoretz today in the NY Post regarding the Bush doctrine of pre-emption:
An unambiguous case for preemption can never be made once the doctrine is invoked and a preemptive war is fought.
Everybody probably agrees that, theoretically, we should have gone to war against al Qaeda before 9/11 to prevent it from happening.
But if we had done so, we never would have known we had succeeded in saving the lives of 3,000 people. The World Trade Center towers would still be standing, their destruction as unimaginable as it was in the minutes before that destruction occurred.
Instead, there would doubtless be arguments about the "mess" we had made of Afghanistan, and about how there was little or no evidence except for cellphone chatter that al Qaeda really had the capacity to inflict major wounds on the American mainland.