Why do people often vote against their own interests?

Why are so many American voters enraged by attempts to change a horribly inefficient system that leaves them with premiums they often cannot afford?  Why are they manning the barricades to defend insurance companies that routinely deny claims and cancel policies?  It might be tempting to put the whole thing down to what the historian Richard Hofstadter back in the 1960s called "the paranoid style" of American politics, in which God, guns and race get mixed into a toxic stew of resentment at anything coming out of Washington.

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