You've got everybody in moral dignity pants—nothing is ever anybody's fault. Look at me, Officer Starling? Can you stand to say I'm evil? Am I evil, Officer Starling?

When she answers that he's destructive, which is the same thing, he offers the counterpoint that if destruction is evil, then storms, hail, and fire are evil—and that all are acts of God. Lector says:

"I collect church collapses, recreationally. Did you see the recent one in Sicily? Marvelous! The facade fell on sixty-five grandmothers at a special Mass. Was that evil? If so, who did it? If He's up there, He just loves it, Officer Starling. Typhoid and swans—it all comes from the same place."

Lector's point, which is carried through the rest of the novel, is that evil isn't always obvious or deliberate. While the evils that Buffalo Bill and Lector pose are studied and deliberate, sometimes evil comes in other forms.

For example, Jack Crawford, the FBI agent in charge of Starling and the Buffalo Bill investigation, is dealing with his sick wife. Though it's not traditional evil, it is a type of evil that fogs his mind as he attempts to work the case. Her illness brings to mind Lector's comment that God causes typhoid. Crawford decides to falsely offer privileges to get Lector to give them information about Buffalo Bill. Though his intentions are good, it allows another problem to take root.

Dr. Chilton, who works at the asylum where Lector is being held, knows that Crawford lied about the transfer. He wants the credit—a selfish motivation—and chooses to offer Lector a different deal that will allow him to move to another institution, which Lector claims to want. While Lector doesn't immediately accept, it sets off a series of events that lead to Lector's escape after he kills his guards.

The characters each want something—promotions, glory, freedom—and work to get those things in ways that aren't completely upstanding. While Buffalo Bill skins women to try to become more like a woman, the rest of the characters all work to their own ends with less gruesome—albeit often unwholesome—methods. 

Many of the characters are flawed or make bad decisions in the novel. Ultimately it's left up to the reader to decide what is evil and what isn't. Harris presents a variety of outright chilling evil and more personal, greedy, and false motivations that drive the characters' decisions. No one is completely innocent, and each reader has to judge the characters for themselves. 

In Thomas Harris' novel The Silence of the Lambs, the main them is relatively subjective. Given that the novel does not have an overlying theme, one can simply interpret what the message of the story is for themselves.

One could easily define any of the following as the main theme of the novel: good verses evil, the search for peace, judging a book by its cover.

For the theme of good verses evil, one only needs to examine the central action of the novel. The FBI is searching for a serial killer and Clarice Starling is assigned to the case. She must come to realize what is good and what is evil in the case, her life, and a key informant, Dr. Hannibal Lecter.

For the theme of one's search for peace, one must examine Starling's character. Readers find out about her past and how she remembers hearing lambs scream when slaughtered. Dr. Lecter brings this up. The screaming of the lambs comes forward into her present. NO longer are the lambs themselves screaming, but her ability to solve the case becomes her screaming lamb. The lambs will only become silent if Starling can solve the serial killer case.

The last theme, the problems associated with judging a book by its cover is relevant with many of the characters of the novel. Some of the characters fit into the immediate justification readers have about a character. Other times, the reader's initial judgement is off.

To define the main theme of the novel, one needs to examine what the novel said to them about the overall message. Therefore, simply decide which theme presented proves to be the one with you, as the reader, most identify with.

The main theme in Thomas Harris's Silence of the Lambs is the nature of evil and the many ways that evil can be acted out. For Clarice Starling, the protagonist of the book, evil is a force that she sees every day in her job as an FBI agent. While investigating the grotesque crimes of the serial killer Buffalo Bill, Starling has to work through the evils of her own life and the evils of serial killer Dr. Hannibal Lecter, her informant.

Unlike the other FBI agents in the novel, Clarice Starling sees the actions of the serial killer through the eyes of the victims. This is a distinct difference that provides her with empathy in direct opposition to evil. Starling's empathy does work to give Dr. Hannibal Lecter, the prime figure of evil as a force of nature, moments of sympathy. In their transactions, Starling and Lecter alter from a balanced relationship of civility to a harshly tenuous working relationship that shows the dichotomy of the innocence versus evil they embody.

Buffalo Bill and Lecter are directly evil despite their differences regarding their civility, but Harris points out that evil can be subtle and less transparent. Lecter makes this point to Starling, stating that evil is not always apparent. Evil can take the form of selfishness (like Jack Crawford) or greed (like Dr. Chilton).

The Silence of the Lambs is a complex novel with likely more than one underlying message. It clearly explores the nature of evil, and it has much to say about the lengths people will go to to get what they need or want. 

One of the book's subjects explores how law enforcement personnel must sometimes negotiate with criminals and deal with the obstructive actions of other involved parties in order to solve crimes and prevent other crimes from occurring. Clarice Starling, though very intelligent and intuitive, is intellectually outmatched by the brilliant Hannibal Lecter, a psychiatrist and imprisoned serial killer.  In exchange for information that lends insight on the serial killer Buffalo Bill, Clarice must not only endure the manipulations of Lecter but also overcome the duplicity and jealousy of Chilton, Lecter's jailer and the director of the hospital for the criminally insane where Lecter is held. 

Lecter's ultimate escape is the outcome of Chilton's incompetence and obstruction, but the combination of Lecter's clues and Starling's intelligence enable her to save Buffalo Bill's final victim.