We offer theory and evidence regarding the impact of content ideology (i.e., emotionally charged beliefs expressed in sentiments) on opinion polarization (i.e., conflicting attitudes about an event) on social media. Specifically, we consider the moderating role of functional affordances and symbolic expressions to draw inferences about opinion polarization. From a sentiment analysis of 3600 posts and a survey of 468 Weibo users, we find that content ideology is positively related to social media opinion polarization. The effect of content ideology is greater when users receive stronger symbolic expressions. Further, our results show an insignificant moderating relationship between functional affordances and this effect. The findings suggest that it is critical to consider content ideology and symbolic expressions when assessing the relationship between published content and polarized opinions on social media.