It is frequently claimed that online disinformation threatens democracy, and that disinformation is more prevalent or harmful because social media platforms have disrupted our communication systems. These intuitions have not been fully developed in democratic theory. This article builds on systemic approaches to deliberative democracy to characterize key vulnerabilities of social media platforms that disinformation actors exploit, and to clarify potential anti-deliberative effects of disinformation. The disinformation campaigns mounted by Russian agents around the United States’ 2016 election illustrate the use of anti-deliberative tactics, including corrosive falsehoods, moral denigration, and unjustified inclusion. We further propose that these tactics might contribute to the system-level anti-deliberative properties of epistemic cynicism, techno-affective polarization, and pervasive inauthenticity. These harms undermine a polity’s capacity to engage in communication characterized by the use of facts and logic, moral respect, and democratic inclusion. Clarifying which democratic goods are at risk from disinformation, and how they are put at risk, can help identify policies that go beyond targeting the architects of disinformation campaigns to address structural vulnerabilities in deliberative systems.