A late entry
One or two highlights:
…experimental data that seem to support the opposite view—including a bunch of very basic and very well-known social psychology results from the 1960’s and 1970’s about bracketing, conformity, and groupthink. They seem to support Overton reasoning: if you don’t voice the “extreme” views, the group tends to converge on a new center position, midway between the views that are voiced. The center thus shifts away from the people who self-censor their (perceived) “extreme” views.
The individual psychology of belief fixation is complicated, and the social psychology is far more complicated. If things were as simple and one-sided as Mooney makes them out to be, politics would be simple, and that’s just false. There are a lot of two-edged swords flying around, for basic, deep reasons.