Of course the darkness in Dickens always contrasts with the light, even though nowadays it is the 'darker' aspects that stand out more in our reading of him. The light usually radiates from young girls who are all the more virtuous and kind-hearted the more steeped they are in a kind of black hell. This emphasis on virtue is the hardest thing to take for modern readers of Dickens.
I. Calvino, 'Charles Dickens: Our Mutual Friend' (1983), in ed. Why read the classics? (1991), tr. M. McLaughlin (1999), 147