I still maintain there are 'trusted employees' out there who are willing and able to deviate from a short final and cause the next attrocities.
Imagine a co-ordinated attack of Boeings being flown into the terminals at JFK, LHR, MAN, ADM etc all within hours of each other.
No need to breach security, no need to hijack, no need for weapons. Probable and credible threat.
Know your enemy, we probably already do know them.