This study examines how platform design influences the tone of user-generated discussions on social media. By conducting a qualitative content analysis of posts and comments related to the Swedish music competition Melodifestivalen 2025, the study compares communication patterns on two platforms owned by Meta: Instagram and Threads. Drawing on Treem and Leonardis (2013) affordance framework and Karahanna et al:s (2018) Needs-Affordances-Features (NAF) model, the analysis reveals clear differences in discussion tonality. Instagram is characterized by short, affective, and affirming expressions, often using emojis and brief statements, while Threads encourages longer, more nuanced discussions, often marked by irony, critique, and argumentation. These differences are linked to affordances such as visibility, persistence, and association, which shape not only what users say but how they say it. Furthermore, the study suggests that different platforms stimulate different psychological needs. While Instagram tends to support relatedness and self-identity, Threads appears to foster autonomy and competence through its design. The results highlight that even platforms with similar technical infrastructure can generate distinct discursive climates based on how affordances are experienced and enacted by users. The study contributes to a deeper understanding of how platform architecture influences digital communication and how tone emerges as a negotiated response to both technological and social structures.