“The effects of conformity on beliefs and attitudes are the more injurious because people tend to associate with others who have similar beliefs to themselves. ... the only way to substantiate a belief is to try to disprove it. But because like mixes with like, people are rarely exposed to counter-arguments to their more deeply held convictions, let alone to counter-evidence. Their beliefs conform to those of their associates: hence, there is little possibility of eliminating persistent errors.”