Social Media Comments

Comments are a central feature of social media platforms, enabling horizontal communication among diverse users. This paper studies how the presence and stance of comments on social media posts affect subsequent on-platform engagement and off-platform attitudes and behavior on socially important issues. For identification, we develop a novel experimental pipeline that manipulates and randomizes comment visibility and stance using Meta's built-in A/B testing infrastructure. In collaboration with a leading racial justice organization, we conduct a large scale field experiment on Facebook reaching a million U.S. users randomly assigned to one of four conditions: (i) no visible comments (control), (ii) opposing, (iii) supportive, and (iv) mixed comments displaying both stances. We find that the presence of a comment section increases engagement with the post. Importantly, comment stance matters: opposing comments significantly amplify reactions, comments, and link clicks relative to the control, whereas supportive comments have little effect. In a complementary artefactual field experiment, we find that comments increase the time spent viewing the post, and exposure to opposing comments leads to more negative perceptions of the organization, less progressive attitudes, and reduced donations. Our results reveal a fundamental trade-off between on platform engagement and off-platform attitudes and behavior, underscoring the importance of platform regulation and governance.