It is a familiar mantra of American politics that the best response to dangerous speech that incites violence and spreads hate is ‘more speech’. Yet the principle obscures at least three crucial questions. Who, in particular, is to undertake the counter-speech that the doctrine recommends? What, exactly, are they required to do? And why is it morally justified to demand that they do it? This article argues that if citizens are to rely on counter-speech to defuse the dangers of dangerous expression, it is not enough to cheerlead its abstract importance and then sit back and hope for the best. Someone needs to do the work, and do it well. The article defends the thesis that all citizens have a moral duty to engage in counter-speech against dangerous expression. Focusing on counter-speech against expression that implicitly or explicitly advocates wrongful criminal violence, it argues that these duties can be derived from a much more basic normative source: the samaritan obligation, held by all moral agents, to rescue others from risks of harm. The specification of these duties’ content, however, depends upon interdisciplinary work that integrates normative theory with social scientific research on human communication.