AT THE SAME time the Internet’s nurturing of niche cultures is contributing to what Cass Sunstein calls “cyberbalkanization.” Individuals can design feeds and alerts from their favorite Web sites so that they get only the news they want, and with more and more opinion sites and specialized sites, it becomes easier and easier, as Mr. Sunstein observes in his 2009 book “Going to Extremes,” for people “to avoid general-interest newspapers and magazines and to make choices that reflect their own predispositions.”