But even as we condemn such violence — particularly political violence like what has just taken place in Arizona — with lamentations and scowls, we persist in condoning it. There are two reasons for our toleration of political violence, despite all our sincere words of grief and castigation. For one thing, America has a long history of political violence — a dark river of brutality, even savagery, that runs through our entire national experience. For another thing, we don’t like facing up to that fact as a people or as a nation. Americans prefer instead to see each outburst of violence — whether in physical attacks on political figures or in blasts of gunfire in our schools and shopping malls — as aberrations, isolated incidents committed by deranged individuals who cause mayhem and slaughter like human whirlwinds. When the wind has subsided, and the casualties have been counted, we proceed as we have done before, dismissing the event as an exception, waiting for the next act of lunacy to occur, at which time we will express our shock and dismay all over again.
http://www.salon.com/2011/01/11/lafantasie_political_violene/