Josh Marshall asks the question,
I tend to agree that if a young person gets on an international flight, not only with no checked luggage but no carry ons that suggest he plans on ever getting off the plane, that is sort of a tip off. But in these cases, I always wonder: Isn't it or why isn't it part of terrorist best practices to just bring some phony luggage? With all the trouble and subterfuge terrorists have to go to get stuff on planes, this seems fairly straightforward. This isn't a criticism of the policies. And obviously Abdulmutallab didn't do this. But in cases like this, I always do wonder: why?I hate to say it, but... probably because it makes it easier to get through security. Nobody's going to be measuring your contraband shampoo as being 3.8 ounces, complaining that your computer has to be in a separate bin apart from its case, or finding a nail clipper with an unacceptably dangerous nail file attached.
Further, when you create a context that leads a significant number of travelers to check all of their luggage, you make it less suspicious when somebody goes through security empty-handed.