Daniel Defoe was writing at a time when the English novel was in its infancy, meaning that the form was not yet clearly established. In other hands, if all the first novelists had taken the moral stance of Richardson, for instance, the novel might have begun as a narrower type of story: a fable of vice punished and virtue rewarded. It is partly because Defoe was a versatile writer with a myriad of interests and a checkered career that the novel began as such an inclusive form.
In Moll Flanders, Defoe makes it clear from the outset that his heroine will not be a model of virtue. The first sentence mentions her familiarity with the criminal courts of the Old Bailey and the prison at Newgate. This is a familiarity shared by the author, who was imprisoned more than once. The question throughout the novel is not whether Moll is vain, licentious, and greedy, since she is clearly all these things and more. The problem for the reader is whether, given her background and circumstances, she could reasonably be expected to be otherwise.
Some readers might feel guilty when reading Moll Flanders, but this does not seem to be Defoe's aim. The reader, after all, is not responsible for the structure of society. However, the reflection that Moll did not create the conditions in which she lives either and cannot be blamed for trying to improve them may incline the reader away from moral judgment and towards understanding.
Condemnation is not a particularly productive attitude, from a literary or philosophical viewpoint. If the reader's main recollection of Moll Flanders is that the protagonist is a bad woman, or even a greedy one, then the novel has not achieved much. However, if the reader has gained some understanding of society and its effects on the individual, then they have learned something and have been made to reflect, which is what the author intends in his depiction of a flawed character's struggle for survival.