How can we comprehensively understand the main concerns and beliefs of the GMO debate in online forums? Genetically Modified Organisms (GMOs) have historically been a hotly debated topic, both within and outside of the agriculture industry. Understanding the complexity of these beliefs can lend policy makers the knowledge necessary to counteract misinformation. In this paper we develop Forumlyze, a systematic framework to understand user beliefs in online discourse surrounding an issue. As a case study, we focus on data collected from Reddit between 2019–2020 from four sub-forums: farming, agriculture, horticulture, and vegetable gardening. In our approach we (a) illustrate the fundamental and temporal characteristics of the issue (b) extract and characterize sentiments surrounding the issue (c) uncover the dominate concepts prevalent in this discussion and the context surrounding these concepts. The comprehensive nature of this analysis led to the following results. (1) The dominant concepts surrounding GMOs are Climate Change, Monsanto and Soil Science. (2) The sentiment of discourse around GMOs and its related concepts indicates a polarized affective system. (3) Evidence that real-world events impact online forum communities' sentiment surrounding GMOs-related concepts.