If I might jump in on the listing of delusions, I think that perhaps one of the most important things to understand about widespread delusions is who, in fact, holds them. A bunch of rednecks in Louisiana not believing in evolution isn't important, because even if they did, it wouldn't inform other parts of their worldview. In general, the specific delusions of ordinary people (IQ < 120) aren't important, because they aren't the ones who are actually affecting anything. Even improving the rationality and general problem awareness of smart people (120 < IQ < 135) doesn't really help, because then you get people who will expend enormous effort doing things like evangelizing atheism to the ordinary people and fighting global warming and the like. Raising the sanity waterline is important, but effort should be focused on people with the ability to actually use true beliefs.