In 2000, the Yale Law Journal published a fascinating article by Cass R. Sunstein titled “Deliberative Trouble? Why Groups Go to Extremes.”
It's about fifty pages long in PDF form. I got about halfway through it a couple weeks ago; have been meaning to post about it, but wanted to finish reading it first. But I may not get around to that for a while, so I'll go ahead and post the link.
The abstract/introduction is fairly short, and gives a reasonably good idea of the topics covered. A couple of excerpts:
[...] The central empirical finding is that group discussion is likely to shift judgments toward a more extreme point in the direction indicated by the median of predeliberation judgments.
[...G]roup polarization is heightened if members have a sense of shared identity. [...G]roup polarization is diminished, and depolarization may result, if members have a degree of flexibility in their views and groups consist of an equal number of people with opposing views.
[...] Like-minded people engaged in discussion with one another may lead each other in the direction of error and falsehood, simply because of the limited argument pool and the operation of social influences.
[...On the other hand, p]artly as a result of group polarization, enclave deliberation can produce positions that would otherwise fail to emerge and that emphatically deserve a public hearing. [...M]embers of low-status groups are likely to be silent in, or silenced by, broader deliberating bodies.
The full article is complicated and covers a lot of ground; I don't think I've entirely wrapped my head around even the half of it that I've read so far. But it's very much worth reading.