why do politicians on both sides feel the need to scare the public with nonsense?

fortunately(or unfortunately) the American public has been trained to respond with, well, nothing... to most folks, the government is like the boy who cried wolf... 4 hours to get through TSA checkpoints starting on Saturday? what happens if it doesn't materialize? people are not going to listen when the government has a real legitimate warning such as NASA discovering a comet heading straight for our planet... well, I take that back, if a comet is heading towards us, I'd appreciate it if the government keeps it quiet.