If people were determined to blow up shopping centers in America they could easily. Pay no attention to the theater security that surrounds your everyday life. It means nothing.
The existence of 'security theatre', the only example I can think of being the TSA, doesn't preclude the possibility that there are real threats.
A related thought: Just because you have spend a lot on security, and there haven't been much in the way of incidents, doesn't mean the security spendings are sensible.