Benedict Anderson's construction of the nation as imagined community makes salient several of Foucault's points on the discourse surrounding sex in a new light. The nation, however, doesn't seem to have a dark side. Talk of the nation is not clearly censored, there does not seem to be a "fundamental prohibition" over the discussion of the nation (Foucault 34). Rather, it seems, the institution of the nation suppresses other possible group formations.
What does the discourse surrounding nation consist of, and what is its secret? Anderson discusses a formative discourse for the nation, the rise of print capitalism and conceptions of "homogeneous empty time" (Anderson 24). The propagation of mass-produced texts (primarily novels and newspapers) enables readers somehow to conceive of simultaneity in a way fundamentally different from before. However, one could easily flip this formulation, and view the rise of print capitalism as a result of our incitement to discourse. The very secret of the nation could be that we (as individuals) cannot truly understand the vastness of the nation, and as such create this expansive discourse to navigate our nations, to somehow master them.
But there is something else repressed by this discourse. It is not simply the unnaturalness of the nation, but any social formation that would stand against it. "[P]ower is tolerable only on condition that it mask a substantial part of itself. Its success is proportional to its ability to hide its own mechanisms" (Foucault 86). And, indeed, the nation-state seems to hide its mechanisms rather well.