We investigate how issue fields with increasing levels of contestation can develop into fields characterized by echo chambers. Studying the introduction of a controversial new approach to addiction services – harm reduction – we explain how proponents’ and opponents’ rhetorical arguments changed over time, transitioning the issue field through different configurations. Our findings reveal how field actors were initially differentiated by moral convictions, and as their expression of moral emotions became more intense, the two groups became increasingly divided and polarized in their views, leading to an issue field characterized by echo chambers. Through our analysis of archival materials and interview data, we explicate this process by identifying three phases of issue field transition: (1) Creating a moral emotional divide; (2) Intensifying antagonization; (3) Insulating against the other side. We contribute to the literature by presenting a model of change explaining how emotional rhetoric, together with different types of triggering events, can fuel increasing levels of contestation and drive the field toward developing echo chambers. Second, by taking a discursive view of issue fields with particular attention to rhetorical arguments, we provide foundational work for an institutional perspective on echo chamber – that echo chambers result from ongoing social processes where people encapsulate themselves based on a sense of right and wrong, in contrast to the predominant view of becoming trapped in an enclosed space. Third, through our focus on the role of moral emotions and how they can escalate in situations of contestation, we advance knowledge regarding the importance of emotions in field dynamics.