Required reading:
http://www.govexec.com/features/0807-01/0807-01s3.htm
What makes terrorism so effective is how it plays on peoples fears. It doesn't matter how likely a terrorist strike is, just so long as the possibility of a terrorist strike can breed fear in the masses. Unfortunately, the US government has also discovered how powerful a motivator this fear can be and has turned it around on its own populace to institute laws and take actions that curb freedoms, with the average Joe on the street believing that the loss of civil rights is an equitable trade in exchange for a perceived higher degree of security.
If you are interested in this general subject, a great place to start is Bruce Schneier's blog:
http://www.schneier.com/blog/
He's one of those people who takes a subject about which you know little to nothing, and makes it fascinating.

