ObjectivesThis theoretical essay attempts to explain, from an interdisciplinary naturalistic perspective that integrates the biological and social sciences, why and how beliefs associated with moral values can lead to dogmatism, intolerant opinions and attitudes, and can motivate violent collective actions. MethodThe article relies on an integrative analysis of the empirical literature, drawing on 138 articles (78% published in the last eight years) in anthropology, neuroscience, psychology, political science, and sociology to explain why and how moralization strongly increases the strength of beliefs and attitudes – in certainty and importance – which, in turn, motivates social engagement and induces attitudinal extremism regardless of ideological or political affiliation. ResultsMoral convictions are perceived as objective, absolute, necessary, universal, and infallible truths with strong links to emotions, the reward circuit, and the value system in the brain that motivates and controls behavior. Moral values are generally shared with other members of one's community and, therefore, linked to social identity. Perceived social consensus is an important input to objectivity. Objectively grounded moral principles generate an expectation of consensus, which can lead to intolerance and hostility regarding anyone who disagrees. Moral convictions motivate participation in collective action and inspire the courage to oppose perceived injustices, real or imagined, despite a personal cost. Cognitive rigidity is often a characteristic of moral convictions. Once an issue is moralized and considered objective, whether in the social, economic, or political domains, it is more likely to be perceived as an absolute belief, held with high confidence, and immune to corrective information. People who are highly confident in their beliefs are more prone to confirmation bias, making them dogmatic with a sense of moral superiority and less willing to seek or consider corrective information regardless of the accuracy of their beliefs. Specific neural signatures and low-level cognitive dispositions are reliably associated with personality orientations prone to political and social dogmatic attitudes. DiscussionOpinions and attitudes, when moralized, can easily make people dogmatic and intolerant. Moral convictions can serve as mandates that facilitate political activism with extreme and often negative views. The conjunction of moral conviction and identity-based ideology is largely responsible for driving the contemporary hostile affective polarization of opinions. The lack of cognitive flexibility explains the failure to update, calibrate, and discard previous beliefs. This metacognitive overconfidence contributes to a dispositional tendency toward dogmatic intolerance. This makes it easier for people who are extreme in their political attitudes, regardless of political affiliation, to perceive their beliefs as moral absolutes (actions are intrinsically right or wrong, regardless of context or consequence) that reflect an objective, universal truth. ConclusionWhen a social, economic, or political issue is moralized, it becomes more difficult to integrate pragmatic aspects that consider risks, benefits, costs, and consequences. Moral convictions are, therefore, a double-edged sword with both constructive and destructive effects. Given that moral beliefs are often associated with the acceptance of any means to achieve preferred goals, a more comprehensive understanding of how and why they promote constructive but also sometimes destructive forms of social engagement is an important program for interdisciplinary scientific research. Moral conviction is a catalyst that turns beliefs into action, for better and for worse.