In that disruptive sense alone, the Web—the protean force of the digital age, the platform that has introduced the tumult and turbulence of media proliferation—has been revolutionary. There has always been more information in the world than there have been news outlets to convey it; but the explosion of outlets, in particular, means that no longer is slant the key self-definitional distinction in news: “I read Daily Kos, so I get my news from a liberal perspective.” Now, the key distinction is about fact: “I read Daily Kos, so I get news that is liberal.” Kos provides its community, often, with completely different information than, say, the National Review Online, or Drudge, or The Washington Post, provide their communities. “The news” itself, as a unitary entity, is no longer something we can take for granted. On the contrary: it is increasingly incoherent—“a mass of niches,” Jeff Jarvis has it. Indeed, the notion of a master narrative itself—the communal melody that, even in its exclusivity, also binds us together in its tunes and tones—is slowly dissolving into white noise.

Again, this isn’t all bad: the benefits of diversity and democratization are clear, and nearly countless. Nor is it all new: the anxieties of the echo chamber are older than the Web itself. But they’re also simplistic. Echo chambers and their ilk, after all—for all their informational exclusivity—also foster, in their very narrowness, passionate beliefs among those who participate in them. And passionate beliefs are good—and necessary—for, among other things, democracy. Beliefs, David Weinberger notes, “aren’t simply propositions to which we assent. They are also the foundation for action and for political solidarity.” And partisan journalism in general, the media scholar Michael Schudson points out, “enlists the heart as well as the mind of the audience. It gives readers and viewers not only information but a cause.”

At the same time, though, echo chambers—even those that many might think of as ‘the good ones’—have an insularity that impedes broader political and cultural discourse. They distort reality through their very presumption of multiple realities. They assume—and, then, foster—a disconnect between sub-truths and, simply, truth. Andrew Leonard put it well when analyzing his shock that the 2004 presidential election—despite the Kerry Confidence of the left-wing blogosphere—ultimately awarded another term to George Bush: “Perhaps if I’d spent less time at Daily Kos and more time talking to people who live in Alabama I’d have been less surprised by the election results,” Leonard writes. “And perhaps I’d be better prepared to deal with them.”

The problem with echo chambers, in other words, isn’t implicit; it’s contextual. Their value depends, as the value of most things depends, on the environment in which they operate: the overall structure of news. And on their ability, in political terms, to balance the will of the minority with the rule of the majority. “I really think I need to get out more, now,” Leonard had it. And: indeed. Niche news is problematic only when the niches are so niche—and so systematized—that diversity itself devolves into cognitive chaos. “Entropy, as loss of meaning,” Orrin Klapp notes, “always lurks at both ends of the continuum from banality to noise.”

The problem occurs, then, when we consumers burrow down into our self-selected spaces within that continuum, drowning out the noise we don’t like in favor of the noise we do. And it occurs even more acutely when we systematize such selective narrowness, writing it into the very DNA of digital journalism. In And Then There’s This: How Stories Live and Die in Viral Culture, Bill Wasik describes the “feedback loop among bloggers and readers,” citing a study finding that 85 percent of blog links led consumers to blogs of the same political bent—“with almost no blog showing any particular respect for any blog on the other side.” In this way, selective exposure becomes a communal activity.

And so, ironically, does cognitive isolation. “If extremism is generated after encountering competing arguments, by all means,” notes the legal scholar Cass Sunstein, who has made extensive studies of crowd dynamics. “The problem is when extremism emerges from the logic of social interactions”—from, in other words, a system of discourse that allows for self-segregation. And that’s the problem we’re seeing, increasingly, in our journalistic infrastructure. On the one hand, people have access to more dissenting views than ever before; on the other, paradoxically, they are more able to ignore those views than ever before. My reality here. Your reality there.

But: what about our reality?

Megan Garber is an assistant editor at the Nieman Journalism Lab at Harvard University. She was formerly a CJR staff writer.