Courts and lawmakers trust psychiatric expertise when making judicial and public policy decisions concerning mental health, but is this trust well placed? This paper adopts a philosophy of science approach informed by medical research to evaluating the validity of psychiatric classification. This provides the basis for an interdisciplinary critical analysis of civil commitment law and use of psychiatric expert witnesses in light of legal evidence standards. This analysis demonstrates that involuntary civil commitment as it now stands is incompatible with broader due process and civil rights concerns and affords an unjustifiable evidentiary status to psychiatric diagnosis.