Morally excused but socially excluded: Denying agency through the defense of mental impairment

Defendants can deny they have agency, and thus responsibility, for a crime by using a defense of mental impairment. We argue that although this strategy may help defendants evade blame, it may carry longer-term social costs, as lay people’s perceptions of a person’s agency might determine some of the moral rights they grant them. Three randomized between-group experiments (N = 1601) used online vignettes to examine lay perceptions of a hypothetical defendant using a defense of mental impairment (versus a guilty plea). We find that using a defense of mental impairment significantly reduces responsibility, blame, and punitiveness relative to a guilty plea, and these judgments are mediated by perceptions of reduced moral agency. However, after serving their respective sentences, those using the defense are sometimes conferred fewer rights, as reduced agency corresponds to an increase in perceived dangerousness. Our findings were found to be robust across different types of mental impairment, offences/sentences, and using both manipulated and measured agency. The findings have implications for defendants claiming reduced agency through legal defenses, as well as for the broader study of moral rights and mind perception.