  The proliferation of radical online communities and their violent offshoots
has sparked great societal concern. However, the current practice of banning
such communities from mainstream platforms has unintended consequences: (I) the
further radicalization of their members in fringe platforms where they migrate;
and (ii) the spillover of harmful content from fringe back onto mainstream
platforms. Here, in a large observational study on two banned subreddits,
r/The\_Donald and r/fatpeoplehate, we examine how factors associated with the
RECRO radicalization framework relate to users' migration decisions.
Specifically, we quantify how these factors affect users' decisions to post on
fringe platforms and, for those who do, whether they continue posting on the
mainstream platform. Our results show that individual-level factors, those
relating to the behavior of users, are associated with the decision to post on
the fringe platform. Whereas social-level factors, users' connection with the
radical community, only affect the propensity to be coactive on both platforms.
Overall, our findings pave the way for evidence-based moderation policies, as
the decisions to migrate and remain coactive amplify unintended consequences of
community bans.
