The focus of concerns about societal fragmentation in public communication is shifting. Instead of the retreat into echo chambers and filter bubbles that had been assumed in previous research, and which has not been confirmed by empirical evidence, greater emphasis is now being placed on polarisation along issue, ideological, and identity lines. Mild forms of polarisation can be productive, but at elevated levels polarisation variously leads individuals to dismiss alternative viewpoints, to attack political opponents verbally and even physically, and to embrace and disseminate (dis)information because of its ideological stance rather than its truthfulness. Social media play a particular role as a public space where such dynamics manifest, and activities there are themselves fed by the posting and sharing of material from mainstream as well as fringe media. This keynote introduces destructive polarisation as a particularly pernicious form of polarisation that is distinguished by a number of distinct symptomatic features; it illustrates these features and their consequences with a case study of the Australian referendum for an Indigenous Voice to Parliament in October 2023, which was affected by a particularly destructive and ultimately successful campaign to polarise the Australian electorate.