llademos, actually the equation should be:
Bomb in a bag not belonging to anybody, put on a plane by someone with access to system = Lockerbie.
All the other cases will just result in confusion, lost bags, perhaps lost flights. Something that happen thousand times each day in the world.
Then, you will see that airlines don't have much of a problem in flying bags (and huge amounts of cargo) without the owner being on the same a/c. Will you claim that it's safe because this stuff is screened? Lucky you if you believe so.
In my opinion it is true that security is routinely used as a blanket excuse for a variety of practices, most of them quite unconveniente for pax, however that is not the subject of this discussion.