I argue that psychopathy undermines three common assumptions typically invoked in favor of moderate reasons responsive theories of moral responsibility. First, I propose a theory of psychopathic agency and claim that psychopathic agency suggests that the systems underlying receptivity to reason bifurcate into at least two sub-systems of receptivity. Next, I claim that the bifurcation of systems for receptivity suggests that reactivity is not “all of a piece” but that it too decomposes into at least two subsystems. Lastly, I argue that prior attempts by Fischer and Ravizza to address these concerns contain an appeal to internalism. Since Fischer and Ravizza want their theory to remain agnostic about the nature of reasons for action, this appeal to internalism is problematic for their view. I close by suggesting that if we are to make sense of when and why psychopaths are responsible then a mechanism-based theory of responsibility must be able to explain how different systems of receptivity and reactivity come together to constitute a single mechanism that grounds responsibility ascriptions for action and they must do so without tacitly appealing to implausible forms of internalism about reasons for action.