[E]cho chambers, made possible by the Internet, can increase (unjustified) extremism, decrease diversity among like-minded people, increase errors, and make people see their fellow citizens as enemies or adversaries in some kind of quasi-war.
The problem with echo chambers is that those who live there tend to end up thinking more extreme version of what they thought before they started to talk – and that is unhealthy for participants and for democracy, at least if people have not heard conflicting views.
I hang out at and participate in a few blogs on both sides of the aisle, and the stark, polarized contrasts in extreme opinions can indeed be shocking. This is often not as apparent in the writing of the blog authors themselves, but truly comes to light in the comments sections, where regular fans of the blogger seem to compete to see who can have the most extreme, biased and often hateful views. Such pile-ons often appear to be a contest to see who can say the most insulting, derogatory things about people who support the opposite political party or espouse different social agendas.
Unfortunately, as the linked interview points out, such conditions are often exactly what people seek out.
It turns out that if people find that others agree with them, they tend to rate those others as more competent and more likable — and that if people find that others agree with them, they tend to rate themselves as more competent or more likable. So there is a natural human tendency to congregate with like-minded types. But from the democratic point of view, that tendency should be resisted.
Far from encouraging dissenting points of view, all too often these blogosphere echo chambers turn into conventions of intellectual grade school bullies. Visitors airing a differing point of view are scorned, insulted, and generally labeled as "trolls" for daring to contradict the prevailing wisdom.
Does this help democracy or advance the political discourse in our country? Just the opposite.