Just possibly there is a double meaning to this exchange. If Teresa's guiding ideal is to see Nostromo (the People) in better standing, then the scornful Monygham's response could mean, "That will never happen on this earth," i.e., it's the nature of man to exploit the People. Note that Monygham dares not look at the Protector of the People when he utters this truth. The clicking lock on the medicine case adds a note of finality.