With today's announcement of a foiled terrorist plot to detonate bombs stowed in carry-on baggage, one really has to ask themselves why terrorists choose to use mass transit as their target for their plots.
I think the answer lies in their motives--to make people afraid and submissive. By blowing up a plane, your killing a couple hundred of people. This has the effect of making people afraid. So afraid, in fact, that they stop flying. That translates into a trickle down effect of people not going about their usual economic activities. Buy a hamburger at the airport, renting a vehicle, purchasing meals at restaurants, buying souvenirs, etc. Terrorism has a large micro-economical impact on those they affect, not to mention the trauma that the world's markets feel in addition.
Terrorism isn't just evil on the grounds of cold blooded murder. Terrorism is evil because it seeks to disrupt the ebb and flow of free economies that have a direct impact on every single person on the planet. That's what 9/11 was all about. I think in the end their desire wasn't necessarily to kill a lot of people, but something far more sinister--destroy the largest symbol of capitalism.
The events after 9/11 certainly prove that it sent our economy into a tailspin. Which, as I have asserted, was their primary goal.
In conclusion, to all you out there that are kidding yourselves about terrorism--it's real and has a direct impact on your life. Before you start criticizing policy on actions taken to prevent it, consider what the real life impact would be without taking those measures.