Greg Mankiw has a great new piece on the economics of media slant. In the last paragraph he discusses the social consequences of individuals choosing to engage in ideological Tiebout sorting. In cliche terms, if Dick Cheney only reads a Texas conservative newspaper while Jerry Brown only reads a liberal Berkeley newspaper (have you read the Berkeley Planet recently?), is society weaker because of this? In this case, people choose to not be exposed to ideas that challenge their pre-conceptions.
Mankiw imagines a better world where there is real competition of ideas rather than people shouting slogans at each other. If people are under-investing in specific activities, then should we subsidize the activity? Should free copies of the WSJ be delivered to everyone in Berkeley? In the language of randomized control trials, would this intention to treat cause "treatment"? Or would the people of Berkeley smoke their copies rather than reading them? What field experimenter can devise a treatment such that those randomly assigned to treatment are "compliant"? What would be the outcome indicator for testing whether cross-pollination leads to a stronger democracy?