Social media's role in the spread and evolution of extremism is a focus of intense study. Online extremists have been involved in the dissemination of online hate, mis- and disinformation, and real-world violence. While the majority of research has focused on right-wing extremism, recent real-world incidents have highlighted the potential for far-left extremists to engage in violence and cause real-world harm as well. In this paper, we present the first large-scale measurement of left-wing extremism on social media. Analyzing 1.3 million posts from 53,000 authors from tankie subreddits, we focus on ``tankies,'' a left-wing community that first arose in the 1950s in support of hardline actions of the USSR and has evolved to support what they call ``Actually Existing Socialist'' countries, e.g., CCP-run China, the USSR, and North Korea. Among other things, our analysis reveals that these groups occupy the periphery of the broader far-left community on Reddit, and their discourse distinctively focus on state-level politics and support for authoritarian regimes, rather than on social justice issues. Finally, we show that tankies have high toxicity scores and use pejorative language, mirroring toxicity patterns reported for other online extremist communities. Our findings provide empirical evidence of the distinct positioning and discourse of left-wing extremist groups on social media.

翻译：社交媒体在极端主义传播与演变中的作用已成为研究焦点。在线极端主义者参与传播网络仇恨、错误与虚假信息以及现实世界暴力活动。尽管多数研究集中于右翼极端主义，但近期现实事件表明极左翼极端分子同样可能参与暴力活动并造成现实危害。本文首次对社交媒体上的左翼极端主义进行大规模测量研究。通过分析来自53,000名用户的130万篇"tankie"（坦克人）子论坛帖文，我们聚焦于这一左翼社群——该群体最早出现于1950年代以支持苏联强硬路线，现已演变为支持其所谓"实际存在的社会主义"国家（如中国共产党领导的中国、苏联和朝鲜）。分析表明，这些群体处于Reddit更广泛极左社区的边缘地带，其话语体系独特地聚焦于国家层面政治与威权政权支持，而非社会正义议题。最后，我们通过毒性评分系统证明坦克人群体具有高毒性特征并使用贬义语言，其毒性模式与其他在线极端主义社群相似。本研究为社交媒体上左翼极端主义群体的独特定位与话语特征提供了实证依据。