I find it hard to avoid hearing a moral double meaning here. Recall that Mrs Gould, the altruist who rode all over the province sympathizing with the suffering people of Costaguana, is here abandoning the bulk of them via the Separationist scheme. Why? To save her husband, is the reason Decoud gave in his letter. But also to save herself, and possibly also to preserve, by saving the mine, the means of her continued altruism. In a sense she, like Charles with his dynamite and Nostromo with his resolve to starve at sea, is ready to sacrifice the purported beneficiaries of a dream-ideal in order to preserve the abstract ideal itself. Note that Decoud, at the end of this paragraph, damns Mrs Gould almost equally with Charles as a fanatic idealist.