It just goes to show that a monster can be disguised as a human. We failed to realize that during Vietnam and it cost a lot of American lives. Many Americans would still allow old gray-haired women to pass unobserved through security areas at airports so we are obviously still on the backside of the learning curve.
It's more that many would rather enjoy a comfortable fantasy than hard unpleasant realities - that our enemies are not bound by the traditional rules of warfare and will use any method at their disposal to get to us.