A light airplane is the last vehicle that would be used for any of those purposes mentioned, because of the lack of payload, lack of accuracy in delivering it, easy detection by the authorities and the high chance of failure. How many light airplanes have been used by terrorists? None. The only comparable case was the Cessna 172 in Florida and all that poor soul managed was to burn out one office in one building.
Lincoln said you can't fool all of the people all of the time but when it comes to "security" I guess he was wrong.