Simply put, Fear. They have been blasted with so much fear for years now by media outlets , that they think just because some guy in Massachusetts shot somebody, that means that its always going to happen I their state of Iowa or whatever. When you listen to so much crap I begins to alter your state of mind. You become what you tune into. They don't want their kid to grow up in the world they "think" exists and they belive it was so much safer "back when they were kids" point is , bad things will always happen, you cant protect your kids forever and the sooner parents realize this the better.