What are the consequences of deceit in Hamlet?

Deceit really drives the plot in Hamlet. The circumstance which generates all further conflict is that Claudius has secretly killed his own brother (and Hamlet's father), which Hamlet's father's ghost conveys to him in act 1. Because of this initial deceit, a tide of deceit follows:
Hamlet feigns madness in order to stall and consider his options for revenge.
Rosencrantz and Guildenstern, once school acquaintances of Hamlet, work with Claudius to deceive Hamlet regarding their loyalty. Their true motive is to assess his state of mind, not to lend support.
Polonius attempts to deceive Hamlet as he spies on a (heated) conversation Hamlet has with his mother. Unfortunately for him, Hamlet realizes that hidden ears are listening, assumes that it is Claudius, and is moved to act on his feelings of revenge—actually accidentally killing Polonius.
Ophelia is played as a pawn by most men in the story, asked to spy for them and to behave in ways that suit their purposes.
Shakespeare crafts the character of Hamlet by using cleverly deceptive puns and wordplay. In the very beginning scenes, Hamlet says of Claudius, "A little more than kin, and less than kind" (1.2.65). Claudius is now both his uncle and his father in law—but not necessarily a kind man or Hamlet's kind of man. When speaking about Claudius to his mother, Hamlet says, "You are the queen, your husband's brother's wife" (3.4.15). Hamlet presents a full logical circle here. Which husband? Which brother? The ability to craft Hamlet's character in this way to showcase the theme of deceit is a testament to Shakespeare's great talents.
Because of deceit, there is great loss of life by the end of the play. Claudius, Gertrude, Laertes, Polonius, Rosencrantz, Guildenstern, and Hamlet himself all meet an untimely end because they choose deceit over truth. The final scenes serve as a reminder that the effects of deceit can be far-reaching, impacting even the innocent (represented by Ophelia).

There is indeed something “rotten in the state of Denmark,” as Marcellus observes to Horatio as the play begins, and one obvious failing in the Danish court is the apparent inability to act without guile. Deceit seems to be the characters’ default behavior; acts of deception riddle the plot, driving it relentlessly to a deadly conclusion. With the exception of Horatio, the only principal characters who don’t die at the end of the play are those who are already dead—Old Hamlet, Polonius, Ophelia, Rosencrantz, and Guildenstern. The dead in Hamlet are all victims of deceit, in one way or another, and with the exception of Old Hamlet, each of them is also guilty of deception.
The catalog of acts of deceit in the play is comprehensive, beginning with the murder of Old Hamlet. In killing the king, concealing the heinous crime, and feigning love for Hamlet, Claudius initiates subsequent events that lead to further deception. Hamlet pretends to be mad in order to verify the truth of his father’s death. Ophelia meets with Hamlet, allowing Claudius and Polonius to eavesdrop on their conversation. Gertrude conspires with Polonius, meeting with Hamlet while Polonius hides in Gertrude's chamber to listen and observe. Claudius schemes to secure Hamlet’s death at the hands of the English king, but through Hamlet’s clever deception, Rosencrantz and Guildenstern die instead after reaching England. It is a final act of deception—Claudius and Laertes’s plotting to draw Hamlet into a duel and kill him with Laertes’s poisoned sword—that results in the ultimate catastrophe that plays out in the drama’s final scene.
Would death and disaster throughout the Danish court have been avoided if Hamlet had chosen at the outset to proceed without guile in addressing his father’s death? Shakespeare seems to suggest that no such option existed for Hamlet, given his nature and the intrigue inherent in the exercise of political power. Moreover, killing a king—even a vile usurper like Claudius—cannot be accomplished without grave ramifications. Regardless of Hamlet’s actions in dealing with Claudius, the consequences would have been severe. The number of characters who die in Hamlet is remarkable, even for a Shakespearean tragedy, and they die as a consequence of deceit.