Have we protected against the motivated terrorist, or only the motivated terrorist on an airplane?
Because over the last 25 years, there have been a _lot_ of "successful" terrorist attacks in the West, and none of them were on planes.
A plane hijacking can evidently cause enormous destruction with minimal equipment and personnel. Even just a bomb on a plane can easily kill 200-500 people depending on the plane’s capacity.
Ground-based attacks since 9/11 have been evidently less effective because a bunch of guys with guns attacking a train station or a rock concert can’t do as much damage as quickly as a hijacker essentially flying a cruise missile into a major office building.