2 Quotes by Hugo Mercier & Dan Sperber

When like-minded people argue, all they do is provide each other with new reasons supporting already held beliefs. Just like solitary reasoners, groups of like-minded people can be victims of belief polarization, overconfidence, and belief perseverance.

[T]wo major features of the production of reasons: it is biased— people overwhelmingly find reasons that support their previous beliefs— and it is lazy— people do not carefully scrutinize their own reasons. Combined, these two traits spell disaster for the lone reasoner. As she reasons, she finds more and more arguments for her views, most of them judged to be good enough. These reasons increase her confidence and lead her to extreme positions.