Echo chamber

The distorting effect of like-minded people talking mainly to each other, without benefit of contrary opinions or outside perspectives.

Said of a community or group becoming more extreme in its views as a result of hearing the same thing over and over.

Use this concept to warn yourself when dialogue starts becoming polarized and you're only hearing one side.

Source: Nathanial Persily, University of Pennsylvania law professor

Related term: Rush Limbaugh's Dittoheads, groupthink