Also see Cass Sunstein on the echo chamber and his new book, #Republic (Princeton University Press Blog)
"In some ways, “#Republic” is a kind of Democracy 101, a review of the basic requirements for those who may have skipped the course. These requirements include, among other things, that citizens be exposed to a wide range of ideas and perspectives—even, and especially, those they would not choose to see or hear. Unplanned, chance encounters—with a protest as one wanders down the street, or a competing argument aired on the evening news—help guard against “fragmentation, polarisation and extremism”. They ensure that people are not hearing only an echo of their own voice. They reduce the likelihood that people will be stirred to extremes, such as terrorism. And they promote shared information and experiences, making it easier to solve problems and govern in a heterogeneous society.
This is the positive side of the free- speech principle, Mr Sunstein writes. It means not only forbidding censorship, but also creating a culture where people engage with the views of fellow citizens. [...]
It is not just up to Mr Zuckerberg, then, to foster a culture of curiosity and openness. Citizens must demand it, Mr Sunstein argues, and they must seek out those serendipitous encounters. “#Republic” is full of constructive suggestions. It should be required reading for anyone who is concerned with the future of democracy—in Silicon Valley and beyond."Social media: In praise of serendipity | The Economist