To benefit from information provided by others, people must be somewhat credulous. However, credulity entails risks. The optimal level of credulity depends on the relative costs of believing misinformation versus failing to attend to accurate information. When information concerns hazards, erroneous incredulity is often more costly than erroneous credulity, as disregarding accurate warnings is more harmful than adopting unnecessary precautions. Because no equivalent asymmetry characterizes information concerning benefits, people should generally be more credulous of hazard information than of benefit information. This adaptive negatively-biased credulity is linked to negativity bias in general, and is more prominent among those who believe the world to be dangerous. Because both threat sensitivity and dangerous-world beliefs differ between conservatives and liberals, we predicted that conservatism would positively correlate with negatively-biased credulity. Two online studies of Americans support this prediction, potentially illuminating the impact of politicians’ alarmist claims on different portions of the electorate.