You overlook the possibility of a trojan horse of the bio weapon kind. Some turd either knowingly or by other means flies in a brings with him/her a plague of some sorts.
They cannot take over planes anymore or smuggle in small nukes but a host of viral weapons can be brought in live.
Kind of scary.
What you say is very true. There have been books written with this scenario.
After the Chinese participation in contaminating pet food, its just a matter of time.
No help from our politicians, though, they are taking money to keep us from protecting ourselves and failing to hold businesses to disclosure standards.
Best guess? The current Congress, both parties, need to be shown the door by the American people!