Does the internet unite and/or divide?

In an article in the New York Times yesterday, David Brooks cited a new NBER paper that challenges the idea articulated by Cass Sunstein (e.g. in Going to Extremes: How Like Minds Unite and Divide) that the internet – with the opportunity it offers users to filter out information they disagree with and communicate exclusively with like-minded communities (ie. homophily) - actually undermines democracy by increasing polarization and blocking the kind of dialogue that can changes minds.  Sunstein,  previously mentioned here in connection with nudges, may or may not be wrong about ideological segregation, but he deserves credit for this excellent paper on Conspiracy Theories (though his proposal to “infiltrate” conspiracy theorist communities alarmed some conspiracy theorists...)