Where in the novel "The Scarlet Letter" does Hawthorne expose assumptions about humanity's moral character?
Hawthorne actually wanted to "expose" some of the flaws in the puritan's ways. Note that he was not necessarily saying that he approved of sin or defended adultry, but he did reveal the hypocrisy of the system.
Hester is forced to live in shame for her sin. It was not enough that she be humiliated publicly, but many of the women thought the punishment was too lenient and that she should be put to death. This would hardly be considered justice.
One cannot help but wonder if Dimmesdale would be expected to undergo the same punishment. He was so beloved by the community. He lived in such guilt that his health began to fail. Was his guilt though for the initial sin or was his guilt that Hester and his daughter had to suffer the consequences and he still lived his normal life.
Although Hawthorne writes about the Puritan era in a later century, his novel suggests that the hypocrisy of religious extremism transcends a particular time and place. Through his portrait of the women of Hester's village in chapter two, Hawthorne shows not only the "severity of the Puritan character" but that their assumptions about other people's moral character are often wrong. The women want Hester to be sentenced to death for her sin, but have no suspicion that their "godly pastor" Dimmesdale was also involved. They assume that their religious leader is incapable of deceit or wrongdoing. For Hawthorne, a place where "religion and law [are] almost identical" is a dangerous place indeed.