This paper reviews the role of discourse in law and public life and identifies threats to the polity from malicious forms of communication. In addition to its role in legal argument, communication is fundamental to public debate in the formation of laws and policies, and it constitutes the social and political fabric through the use of forms of address and recognition of others. This argument builds on aspects of discourse theory and feminist and other critiques of it that suggest that it applies to a narrow community of discourse, and so excludes other cultures. It takes a broad view of participants in public debate, which necessarily crosses national and cultural borders. Responsible communication demands that we argue in good faith, truthfully and coherently, and that we recognize our partners in discussion, both for who they are and for their place in a shared community. The paper argues that public discourse has sunk to dangerous levels in the present century, citing examples of bad faith, provocation and insult from Australian prime ministers (2002, 2015) and presidential candidates in France (2005) and the United States (2016). It concludes that lying, incoherence, self-contradiction, insult and injury fall outside the bounds of public discourse. Rapid communicative intervention is needed to identify each of these malicious forms of communication as a betrayal of the civic public, before it provokes the next vicious response.