Dickens makes Fagin and Sikes horrific by having them target sweet, innocent Oliver.
Sikes and Fagin are both very greedy. Each is violent, sneaky, and self-centered. Fagin knocks Dodger down the stairs, and Sikes hits Nancy.
Fagin is described as “villainous-looking and repulsive” (ch 8). Although most of the descriptions of Fagin are dripping with sarcasm, it is clear to the reader that he is anything but “virtuous.”
Whenever the Dodger or Charley Bates came home at night, empty-handed, he would expatiate with great vehemence on the misery of idle and lazy habits; and would enforce upon them the necessity of an active life, by sending them supperless to bed. (ch 10)
Fagin takes in boys, and teaches them to be criminals. He treats them well when they are making money, and with neglect and abuse the rest of the time. Oliver does not realize this, though he notes that Charley Bates has “very loose notions concerning the rights of property.” It is not until he actually sees the boys steal handkerchiefs that he realizes what they are doing, and the unwitting part he has played in it.
Although the reader might be annoyed at Fagin, it is not hard to be downright horrified at Sikes. We are first introduced to Bill Sikes when Dodger and Charley come home without Oliver and tell Fagin he’s been captured. Sikes is scowling, dirty, and mean. He kicks his dog and hits his girl. Like Fagin, he takes advantage of Oliver. He forces Nancy to help him take the boy back, so he won’t tell on them.
Fagin and Sikes both act in their own best interests at all times. Although they are pathetic figures, they are also low criminals. They kidnap Oliver, force him to break into Brownlow’s house, and threaten his life. The reader is horrified by these two men, and glad when they are both arrested and hanged (although Sikes hangs himself).