This essay uses insights from the study of risk perception to remedy a deficit in liberal constitutional theory—and vice versa. The deficit common to both is inattention to cognitive illiberalism—the threat that unconscious biases pose to enforcement of basic principles of liberal neutrality. Liberal constitutional theory can learn to anticipate and control cognitive illiberalism from the study of biases such as the cultural cognition of risk. In exchange, the study of risk perception can learn from constitutional theory that the detrimental impact of such biases is not limited to distorted weighing of costs and benefits; by infusing such determinations with contentious social meanings, cultural cognition forces citizens of diverse outlooks to experience all manner of risk regulation as struggles to impose a sectarian orthodoxy. Cognitive illiberalism is a foreseeable if paradoxical consequence of the same social conditions that make a liberal society conducive to the growth of scientific knowledge on risk mitigation. The use of scientific knowledge to mitigate the threat that cognitive illiberalism poses to those very conditions is integral to securing the constitution of the Liberal Republic of Science.