Though a large body of past research shows how religion can prompt us toward saintlike behaviors, our review found that it has neglected the ways that religion can also turn us into sinners. Highly religious people tend to be more intolerant of people with different ideologies and ethnicities, and report greater aggression and revenge-seeking than nonbelievers. Instead of showing group commitment through self-sacrifice like cooperators, crusaders—just like the Catholic Crusaders of the eleventh through thirteenth centuries—reify their religious communities by harming others. Crusaders are motivated by religious tribalism: the aspects of religion that bind people into tight-knit but noninclusive communities. Religious groups like the Westboro Baptist Church, who preach hate and vitriol against nonbelievers (and especially the LGBTQ+ community), exemplify the same hostile group loyalty that characterizes crusaders.
