This study examines the #MeToo movement in South Korea to understand the role of online platforms in the development of a backlash discourse. We apply computational methods to analyze how the #MeToo movement was discussed by citizens on Twitter and in online news comments, in contrast to the traditional news media. Our findings show that the public discourse in user-driven online platforms enabled the proliferation of a disparaging narrative that challenged the movement, while the patterns of the backlash differed across platforms. Using word-embedding techniques and network analyses, we illustrate the shift in frames around #MeToo movement and highlight how platform affordances meaningfully shaped the way the backlash unfolded.