  When toxic online communities on mainstream platforms face moderation
measures, such as bans, they may migrate to other platforms with laxer policies
or set up their own dedicated websites. Previous work suggests that within
mainstream platforms, community-level moderation is effective in mitigating the
harm caused by the moderated communities. It is, however, unclear whether these
results also hold when considering the broader Web ecosystem. Do toxic
communities continue to grow in terms of their user base and activity on the
new platforms? Do their members become more toxic and ideologically
radicalized? In this paper, we report the results of a large-scale
observational study of how problematic online communities progress following
community-level moderation measures. We analyze data from r/The_Donald and
r/Incels, two communities that were banned from Reddit and subsequently
migrated to their own standalone websites. Our results suggest that, in both
cases, moderation measures significantly decreased posting activity on the new
platform, reducing the number of posts, active users, and newcomers. In spite
of that, users in one of the studied communities (r/The_Donald) showed
increases in signals associated with toxicity and radicalization, which
justifies concerns that the reduction in activity may come at the expense of a
more toxic and radical community. Overall, our results paint a nuanced portrait
of the consequences of community-level moderation and can inform their design
and deployment.
