A broader danger of unverifiable beliefs is the temptation to defend them by violent means. People become wedded to their beliefs, because the validity of those beliefs reflects on their competence, commends them as authorities, and rationalizes their mandate to lead. Challenge a person's beliefs, and you challenge his dignity, standing, and power. And when those beliefs are based on nothing but faith, they are chronically fragile. [...] Since one cannot defend a belief based on faith by persuading skeptics it is true, the faithful are apt to react to unbelief with rage, and may try to eliminate that affront to everything that makes their lives meaningful.
Steven Pinker, The Better Angels of our Nature, p. 140