While crowdsourcing approaches in content moderation systems increase the governance capacity of social media, they also offer a loophole for malicious users to massively report and restrict disliked content.To fill the knowledge gap about large-scale, bottom-up attempts at restraining online expressions, we focus on a type of public and institutionalized mass reporting: anti-smear (反黑) campaigns within Chinese online fandom communities, where fans coordinate together and collectively report content they perceive as inappropriate.Based on detailed data of more than two hundred anti-smear groups collected from Weibo and interviews with active participants, our paper examines the motives and dynamics of anti-smear campaigns, the coordination strategies used to game the content moderation system, and the diffusion of anti-smear culture among fandom networks. We argue that anti-smear is essentially a practice of information control and reflects an intolerant mindset of social media users towards dissidents.This paper also points out the vulnerability of community-based content moderation systems to be weaponized in a polarized age, which brings great challenges to platform governance.

While crowdsourcing approaches in content moderation systems increase the governance capacity of social media, they also offer a loophole for malicious users to massively report and restrict disliked content. To fill the knowledge gap about large-scale, bottom-up attempts at restraining online expressions, we focus on a type of public and institutionalized mass reporting: anti-smear (反黑) campaigns within Chinese online fandom communities, where fans coordinate together and collectively report content they perceive as inappropriate. Based on detailed data of more than two hundred anti-smear groups collected from Weibo and interviews with active participants, our paper examines the motives and dynamics of anti-smear campaigns, the coordination strategies used to game the content moderation system, and the diffusion of anti-smear culture among fandom networks. We argue that anti-smear is essentially a practice of information control and reflects an intolerant mindset of social media users towards dissidents. This paper also points out the vulnerability of community-based content moderation systems to be weaponized in a polarized age, which brings great challenges to platform governance.