Online platforms face pressure to keep their communities civil and
respectful. Thus, the bannings of problematic online communities from
mainstream platforms like Reddit and Facebook are often met with enthusiastic
public reactions. However, this policy can lead users to migrate to alternative
fringe platforms with lower moderation standards and where antisocial behaviors
like trolling and harassment are widely accepted. As users of these communities
often remain \ca across mainstream and fringe platforms, antisocial behaviors
may spill over onto the mainstream platform. We study this possible spillover
by analyzing around $70,000$ users from three banned communities that migrated
to fringe platforms: r/The\_Donald, r/GenderCritical, and r/Incels. Using a
difference-in-differences design, we contrast \ca users with matched
counterparts to estimate the causal effect of fringe platform participation on
users' antisocial behavior on Reddit. Our results show that participating in
the fringe communities increases users' toxicity on Reddit (as measured by
Perspective API) and involvement with subreddits similar to the banned
community -- which often also breach platform norms. The effect intensifies
with time and exposure to the fringe platform. In short, we find evidence for a
spillover of antisocial behavior from fringe platforms onto Reddit via
co-participation.

该研究使用差异法设计来研究被 Reddit 和 Facebook 封禁的三个社区迁移到边缘平台的用户，并发现与这些社区共同参与可能导致用户在 Reddit 上的毒性言论和违反平台规范的行为增加，并随着时间和曝光度而加剧。

边缘平台上的反社会行为外溢：社区封禁的无意后果

Spillover of Antisocial Behavior from Fringe Platforms: The Unintended Consequences of Community Banning

While online social media offers a way for ignored or stifled voices to be
heard, it also allows users a platform to spread hateful speech. Such speech
usually originates in fringe communities, yet it can spill over into mainstream
channels. In this paper, we measure the impact of joining fringe hateful
communities in terms of hate speech propagated to the rest of the social
network. We leverage data from Reddit to assess the effect of joining one type
of echo chamber: a digital community of like-minded users exhibiting hateful
behavior. We measure members' usage of hate speech outside the studied
community before and after they become active participants. Using Interrupted
Time Series (ITS) analysis as a causal inference method, we gauge the spillover
effect, in which hateful language from within a certain community can spread
outside that community by using the level of out-of-community hate word usage
as a proxy for learned hate. We investigate four different Reddit
sub-communities (subreddits) covering three areas of hate speech: racism,
misogyny and fat-shaming. In all three cases we find an increase in hate speech
outside the originating community, implying that joining such community leads
to a spread of hate speech throughout the platform. Moreover, users are found
to pick up this new hateful speech for months after initially joining the
community. We show that the harmful speech does not remain contained within the
community. Our results provide new evidence of the harmful effects of echo
chambers and the potential benefit of moderating them to reduce adoption of
hateful speech.

本文以 Reddit 社区为例，测量加入具有仇恨言论的极端社区对该社交媒体平台中仇恨言论传播的影响，研究发现加入这种社区会导致恶意言论在平台上传播，并且这种负面影响会持续数月，为降低仇恨言论传播的风险，有必要对这些 “回音室” 进行管理。