The Unionist Garibaldi would indeed look dimly at Decoud's skepticism, which has led to the Separatist movement now going on. Conrad is establishing the dark night here in preparation for Decoud and Nostromo's voyage, but it also has a symbolic meaning: the darkness of the Placid Gulf represents the space between souls, and Separatism, by emphasizing the differences between subjective natures, brings this darkness to the forefront.