Despite decades of anti-caste efforts, sociocultural practices that marginalize lower-caste groups in India remain prevalent and have even proliferated with the use of social media. This paper examines how groups engaged in caste-based discrimination leverage platform affordances of the social media site X (formerly Twitter) to circulate and reinforce caste ideologies. Using a critical discourse analysis (CDA) approach, we examine the rhetorical and organizing strategies of 50 X profiles representing upper-caste collectives. We find that these profiles leverage platform affordances such as information control, bandwidth, visibility, searchability, and shareability to construct two main arguments: (1) that their upper caste culture deserves a superior status and (2) that they are the "true" victims of oppression in society. These profiles' digitally mediated discursive strategies contribute to the marginalization of lower castes by normalizing caste cultures, strengthening caste networks, reinforcing caste discrimination, and diminishing anti-caste measures. Our analysis builds upon previous HCI conceptualizations of online harms and safety to inform how to address caste-based marginalization. We offer theoretical and methodological suggestions for critical HCI research focused on studying the mechanisms of power along other social categories such as race and gender.