  Social media networks commonly employ content moderation as a tool to limit
the spread of harmful content. However, the efficacy of this strategy in
limiting the delivery of harmful content to users is not well understood. In
this paper, we create a framework to quantify the efficacy of content
moderation and use our metrics to analyze content removal on Facebook within
the U.S. news ecosystem. In a data set of over 2M posts with 1.6B user
engagements collected from 2,551 U.S. news sources before and during the
Capitol Riot on January 6, 2021, we identify 10,811 removed posts. We find that
the active engagement life cycle of Facebook posts is very short, with 90% of
all engagement occurring within the first 30 hours after posting. Thus, even
relatively quick intervention allowed significant accrual of engagement before
removal, and prevented only 21% of the predicted engagement potential during a
baseline period before the U.S. Capitol attack. Nearly a week after the attack,
Facebook began removing older content, but these removals occurred so late in
these posts' engagement life cycles that they disrupted less than 1% of
predicted future engagement, highlighting the limited impact of this
intervention. Content moderation likely has limits in its ability to prevent
engagement, especially in a crisis, and we recommend that other approaches such
as slowing down the rate of content diffusion be investigated.
