Small aircraft including crop dusters cannot carry enough weight and are too easily traced. I do not know of single case or attempted use of light aircraft in terrorist activity. It just isn't practical or efficient.
Terrorist prefer suitcase bombs, suicide bombers, car bombs and truck bombs for a reason.
It doesn't matter. The truth is, General Aviation is one of the few remaining bastions of freedom. That is something that the
Terminally
Stupid
Assholes can't stand. Currently those flying GA don't have to be grappled, fondled, pawed at, and forced to go through their electronic peep show.
Look for this to be the reason they use to try to include GA in their perversions . . . errr . . . I mean Inspections.