A positive bias of opinions has frequently been identified across online review websites, suggesting that the public is making decisions based on a limited range of opinions. While scholars often attribute this bias to social loafing or self-selection, this study investigates the positive bias from the perspective of opinion expression. Drawing from the spiral of silence theory, a qualitative analysis of discussion forums reveals that fear of isolation reduces the willingness of members to voice neutral and negative reviews. Additionally, communicative affordances of the interface were found to further suppress neutral and negative opinions. These results extend the spiral of silence theory into the context of non-anonymous multichannel communication platforms and indicate the need to consider the role of communicative affordances in online opinion expression.