Nature... is nothing but the inner voice of self-interest.

Taken at face value, the line rejects the Romantic idea that “nature” is a pure moral guide. Instead, it suggests that what people call nature often masks a more basic impulse: self-preservation, appetite, and advantage. In this view, appeals to “natural” feeling or “natural law” are not automatically ethical; they can be rationalizations for egoism. The ellipsis underscores a polemical tone—“nature” is being stripped of its halo and reduced to motive. Read in a Baudelairean key, the remark aligns with his suspicion of sentimental moralizing and his interest in the darker, conflicted springs of human desire.