The focus of The House of the Seven Gables is on two great crimes: first, Colonel Pyncheon's false accusation of Matthew Maule for witchcraft, and second, Judge Pyncheon's framing of Clifford for murder. But the emphasis isn't on the forensics of these two crimes (this isn't Bones); instead, Hawthorne looks at the psychology that allows guys like Colonel and Judge Pyncheon to ruin others' lives and feel no guilt. Not only do they not feel bad, they actually think they are upstanding, virtuous members of the community. So what's the source of this disconnect? Hawthorne considers several factors: family background, heredity, and public approval all play a role.
Phoebe's extreme respect for the law underlines her symbolic connection to the home and to settling down, while Mr. Holgrave's participation in different reform movements of his day highlights his association with movement and progress.
Judge Pyncheon's inability to feel guilt allows him to behave immorally; as a result, we can argue that the ethical basis of The House of the Seven Gables is guilt.