This opinion paper focuses on foregrounding the issue of the hidden curriculum in L2 writing and how addressing its negative sides can greatly move forward our understanding of students' writing learning experiences and further promote more effective and equal writing teaching. Specifically, this paper argues that the negative sides of the hidden curriculum could partially account for students' dissatisfying writing development and unpleasant writing learning experiences and discusses its possible harm to educational effectiveness and equality. The paper then outlines recommendations for future research and proposes strategies for teaching practitioners to better handle the hidden curriculum.