The deep ocean is increasingly featured in climate solution discussions. An emerging narrative suggests that marine carbon dioxide removal (mCDR) is essential to meet global climate targets. The argument made is similar to claims that deep-seabed mining (DSM) is necessary to enable widespread electrification, in that both are framed as helping to address climate change. We compare the structure and history of these narratives, highlighting that while potential negative impacts on marine life have emerged as a central feature in debates about DSM, environmental and social risks associated with mCDR are yet to receive similar recognition. In light of this comparison, we argue that potential harm needs to be further emphasized in considerations of deploying mCDR.