From Schneier on Security:
Terrorism sounds easy, but the actual attack is the easiest part.
Putting together the people, the plot and the materials is hard. It’s hard to sneak terrorists into the U.S. It’s hard to grow your own inside the U.S. It’s hard to operate; the general population, even the Muslim population, is against you.
Movies and television make terrorist plots look easier than they are. It’s hard to hold conspiracies together. It’s easy to make a mistake. Even 9/11, which was planned before the climate of fear that event engendered, just barely succeeded. Today, it’s much harder to pull something like that off without slipping up and getting arrested.
But even more important than the difficulty of executing a terrorist attack, there aren’t a lot of terrorists out there. Al-Qaida isn’t a well-organized global organization with movie-plot-villain capabilities; it’s a loose collection of people using the same name. Despite the post-9/11 rhetoric, there isn’t a terrorist cell in every major city. If you think about the major terrorist plots we’ve foiled in the U.S. — the JFK bombers, the Fort Dix plotters — they were mostly amateur terrorist wannabes with no connection to any sort of al-Qaida central command, and mostly no ability to effectively carry out the attacks they planned.
The successful terrorist attacks — the Fort Hood shooter, the guy who flew his plane into the Austin IRS office, the anthrax mailer — were largely nut cases operating alone. Even the unsuccessful shoe bomber, and the equally unsuccessful Christmas Day underwear bomber, had minimal organized help — and that help originated outside the U.S.