Designed for discourse: how reactions and replies create trade-offs in political participation

While social media platforms aim to foster quality discussions through interactive features, existing theories often overlook how these features may produce divergent outcomes. We build on the Theory of Interactive Media Effects model to study how interactive features affect emergent user behavior and interaction patterns. Through an experiment (N = 1,370) on a custom-built platform, we tested how two common features—reactions and replies—influence participation, engagement, and diversity in political discussions. Our findings reveal a fundamental trade-off between these features. Reaction features, which are inherently low-effort, enabled quick responses but reduced overall message volume, while simultaneously increasing the elaboration of individual posts and exposure to diverse viewpoints. In contrast, reply features, which are inherently high-effort, supported targeted exchanges but deepened interactions within narrow threads, fragmenting conversation and reducing group-level diversity. Our findings demonstrate that while interactive features may facilitate interaction, they structure trade-offs between different forms of inclusiveness, thereby offering new insights for theorizing and designing more equitable platform mechanics.