There certainly are people and organizations inside and outside the government who want people to be afraid. Martha Stout's "The Paranoia Switch"* looks at politicians who exploit this reaction and how the media contributed to the environment after 9/11. And the "surveillance-industrial" complex makes their money (and keeps their power) based on fear.
* good summary/review at http://www.sott.net/articles/show/142725-Limbic-Warfare-and-...
It's similar to the state of "tough on crime" policies like 3 strikes and mandatory minimum sentences - even when proven ineffective no one wants to reverse the statutes for fear of being seen as weak on crime.