Moral behavior and legal institutions coevolve. While evolutionary game theory has often analyzed the evolution of moral behavior within given institutional rules, it has not examined the coevolution of moral preferences and different institutional aspects of the decision environment. By an ‘indirect’ evolutionary approach, we analyze the coevolution of moral preferences (in the sense of trustworthiness) and legal institutions like court rulings and legal insurance. We find that preference detection capabilities crowd in morality and can thus render useless the role of courts and legal insurance as public institutions. Legal institutions become crucial for the emergence of morality, however, when information about preference types is not available. This holds true even when courts do not have superior detection capabilities than other agents.