  Should social media platforms override a community's self-policing when it
repeatedly break rules? What actions can they consider? In light of this
debate, platforms have begun experimenting with softer alternatives to outright
bans. We examine one such intervention called quarantining, that impedes direct
access to and promotion of controversial communities. Specifically, we present
two case studies of what happened when Reddit quarantined the influential
communities r/TheRedPill (TRP) and r/The_Donald (TD). Using over 85M Reddit
posts, we apply causal inference methods to examine the quarantine's effects on
TRP and TD. We find that the quarantine made it more difficult to recruit new
members: new user influx to TRP and TD decreased by 79.5% and 58%,
respectively. Despite quarantining, existing users' misogyny and racism levels
remained unaffected. We conclude by reflecting on the effectiveness of this
design friction in limiting the influence of toxic communities and discuss
broader implications for content moderation.
