Echo chamber
From Conservapedia
An echo chamber is a hollow enclosure used to echo sounds, primarily used for recording purposes.
Figuratively, it is a group of people, especially in the liberal media, who quote only one another and refuse to consider outside information or viewpoints, or a Web site catering to such a group. Another term is hugbox, which has the added implication that the editors or moderators actively enforce conformity of viewpoint.
