The moral shallowness objection contends that libertarianism seems plausible only in the absence of a robust understanding of the nature of moral responsibility. P.F. Strawson's work is the fount of this objection. In response I argue, surprisingly, that Strawson's account of the nature of responsibility, according to which the essence of responsibility is defined in terms of the reactive attitudes (such as gratitude and resentment), actually leads to libertarianism about its conditions of application. In defense of this contention I offer a theory of the normative force of excuse which shows that moral responsibility requires that agents have free will. I then construct the No Opportunity Argument which demonstrates that free will, and thus moral responsibility, is incompatible with determinism.