On the surface, this is mere politeness at an awkward conversational moment (the
doctor has all but admitted his self-loathing aloud). But there is another reason
why the altruist Mrs Gould might shy away from that particular statement. Seen
on the large scale, altruism can be described as the effort of the oppressing
class to think of other people so much better than it is able to think of itself.
If Mrs Gould were to accept Monygham's logic, then she would see no point in uplifting
the downtrodden, because once uplifted they would likely trod someone else down
in their turn. In this little, almost wordless exchange Conrad lays out the fundamental
conflict between altruism and cynicism.