What's remarkable about Little Dorrit is that there doesn't seem to be an overarching system of morality that governs the actions of the characters. Instead, almost every single individual has his or her own code of ethics – many of which contradict and conflict with each other. The upshot of this setup is that most actions have several valid-seeming interpretations, and there is no completely neutral authority to make judgment calls about fair play. All the reader can do is wait for the chaos to settle and see who remains standing in the rubble.
Because this novel is deeply pessimistic about the state of the world, most of its ethics boil down simply to "might makes right."
The novel shows us a world where almost everyone in some way lives by the "diseased arithmetic" of Gowan or the paranoia of Miss Wade. Believing in the goodness of others is a luxury that tends to punish those who hold the belief.