You would also have to assume there were no other major terrorist-related aviation catastrophes since 9/11...
As a primer, airport security was controlled by the airlines. In a way, I feel we're all probably safer now with the TSA running security. They haven't caught any terrorists because most terrorists realize their odds of success with airline-related incidents is substantially reduced.
Of course, the TSA is also an example of an over-zealous government agency invading many Americans' privacy rights. So, there's that.