Most people ignore things whose risk could not be determined. In their mind, they divide issues into what can be estimated and what can not be. Then they spend time on estimating the risk of things that they can estimate. So much of the mind share is taken by things that can do something about, the risks of things they could not estimate gets relegated into some corner.
Some sort of, "we can't do anything about it anyway, so why think about it or talk about it?". That is how people get blindsided. Remember Mitt Romney talking about "there are this 47% we can't do anything about" (I admit what he was trying to convey was not the as bad as the media made him out to be, I am a staunch Democrat by the way). That is a classic top executive way of dealing with things. "Cant do anything about it, forget and concentrate on something we can do about".
But that is precisely where people will attack us. For an enemy of America the first question is, "What is something they can't do anything about? Let us attack there. They can't make every liberty loving American to subject themselves to strip search, gate rape. Meekly walk barefoot in front of uniformed officers? They will get flashbacks of cattle cars and nazis with folding tables snapping 'papers, please'. That for just boarding a plane to fly to Kalamazoo! come on! They cant do that. So let us hijack a plane and hit a couple of buildings."