The real scenario that should greatly concern us is commercial cargo transported on passenger airliners. The vast majority of commercial cargo - the figure I have seen most often is 80% - is not screened. Many airlines transport such unscreened cargo on passenger flights. FedEx, DHL, etc. often essentially charter space on passenger airliners for some of their packages. I understand that some international flights carry large quantities of cargo, as opposed to checked bags. Think of the real purpose of TSA - Kabuki security - and this failure to screen cargo with the same zeal as the screening of passengers makes sense.