I think it is not just uncertainty per se, but uncertainty vis a vis expectations. Few peoples in the world (outside Western Europe) enjoy the same level material stability that all but the handful of homeless people in this country do. Yet they do not feel threatened and trapped the way many people in this country do.
I think what explains is the schizophrenic nature of the US society. On the one hand, it creates an illusion and expectation of security by lavish outpour of security fetishes - from countless insurance schemes, to crime prevention measures, to the regulation of every aspect of the everyday life and to elaborate hedging schemes against all kinds of risk. On the other hand, this society is bombarded with a constant barrage of fear mongering and threats to sell something: from political candidates, to automobiles, houses, security gizmos, insurance products, cultural products, to remedies, snake oil and what not.
So here you have it people who are told that they live in a society that has the greatest level of security ever created and at the same time every aspect of their everyday life is threatened by a message form the army of advertisers, commodity peddlers, newscasters, political campaigners, moral entrepreneurs. Hence the pervasive sense of insecurity amidst one of the most safe and prosperous environments on Earth.
Wojtek