After the December "underwear bomber" incident I realized that Al Qaeda did not really want to blow up the plane, but rather they wanted the U.S. to believe that it was a failed attempt.
Suppose that the "bombing attempt" had succeeded. A bomb would be the immediate suspected cause, and likely Al Qaeda would have taken credit. But, it would take an investigation to determine cause, they might not be able to determine with certainty that it was a bomb, and unless they found pieces of a man's genitals splattered around the plane they would not know where the bomb had been hidden.
Now, look at the results of this and previous "failed" attempts, presuming Al Qaeda's goal is to maximize the impact on our lives. After the "shoe bomber" we had to remove our shoes to go through security. Al Qaeda would know the explosive they used could not be easily set off, and would probably know from reports that even if it had exploded the damage would likely not have been catastrophic.
I imagine the Al Qaeda leadership sitting around making fun of us; thousands upon thousands taking off their shoes just to get on a plane, and someone says "I wonder if we could get them to take off their clothes!" After they stop laughing, one of them on a sleepless night gets an idea. "Of course. Exploding underpants."
Though that conversation is fantasy, look at the results. We are so accustomed to being unreasonably searched without cause that many are willing to be virtually stripped naked by a stranger on a machine with a hard drive on the promise that the image will be destroyed.
I believe that these "failed" attempts are also in the interest of some in our government. There was a study of what average people could come up with to defeat our security, so they know that any steps they take can be defeated. So why is there a rush to implement virtual strip searches, except that they have the technology and were looking for an excuse?
I will conclude with this. Let us hope that no one tries to set off a tampon bomb.