I'm not sure I understand

I don't really understand the purpose in cancelling flights for security reasons. It seems that the recent spate of cancellations serve to provide potential terrorists with an understanding of how good or bad our intelligence is. The terrorists are being successful in impacting our daily lives. It would seem that if you have good intelligence about a plot that one's best bet would be to equip the plane to handle it. Put air marshals, or their foreign equivalents on the plane, triple check the baggage, take the cargo off the flight. Perhaps airlines should start cargo swapping. To prevent people from putting things in bags and then finding their way to a cargo hold in flight, swap bags with another plane randomly. Sure they need to be destined for the same spot at about the same time but it puts the control back in the hands of the airlines and puts terrorists, not ordinary people, off guard.