The Airline Pilots Association (ALPA, the largest pilots union) has petitioned the FAA to give pilots total control over security decisions when on the ground. Currently, airline employees and the TSA control decisions when the plane is parked at the gate, and the Captain has final authority in the air.
My unsupported hunch? If you give this authority to pilots, it will be used in work slowdowns. Rather than a safety measure, it’s a way of amassing leverage for union bargaining. Just as pilots might work slowly before and after takeoff, and mechanics might ground flights for minor transgressions that don’t effect safety, pilots would now be able to use their own judgment and decide to cancel a flight for “security reasons.”
Maybe I’m just paranoid…