Computer science needs to be sustainable, and CS educators have an important role to play in changing the discipline. Recent efforts have emerged to teach CS in ways that apply computing to mitigate climate change, but this alone is insufficient: we must also change what it means to do computing. We use duoethnography to interrogate our practices as CS educators to support the goal of integrating sustainability into CS. Despite being invested in these goals, we each realized that we had been nevertheless reinforcing the cultural norms that underpin the environmental and social damage caused by computing. We found five themes in the qualitative analysis of our reflections: (1) A lack of materiality in CS classes makes it difficult for computer scientists to scrutinize the environmental costs of hardware, (2) The discourse on “greenness” in computing neglects the role of embodied emissions, (3) The lack of context in CS education teaches students to perceive the status quo as “natural", (4) Those who have bought into the dominant ideology of CS can be resistant to innovating CS education, and (5) Materiality helps with teaching computing. We illustrate how changing CS to become more sustainable requires deeper thought than “add sustainability and stir” to the curriculum, and insights toward addressing the root ideology of CS education.