This country has never been attacked on its own land by an outside force. We've never had to fear life in our own country, although warnings against travel abroad have been issued a few times through the years. House burglars, purse snatchers and armed robbers have been among our greatest threats, but reasonable precautions severely reduce the odds. Terrorism, especially bioterrorism, is something we never considered we would face. But our response should be little different than our approach to any potential danger.
People have a wide range of risk tolerance.
The high wire walker and the stunt pilot have a common threshold, the same for emergency and public safety workers. The average citizen takes risks daily, but adjusted to them long ago. To thwart burglars, we lock our houses and cars. To keep from drowning, we wear life preservers on boats. We buckle up in cars.