How is Hamlet led by evil?

While I think that some of Hamlet's deeds were cruel, I don't think evil is what led him to commit those acts. In Act 3, sc. 4, when Hamlet kills Polonius, his words indicate that he thought it was the king hiding behind the arras and so killing him would have fulfilled his father's ghost's request for vengeance.  Also, in this scene, Hamlet is highly incensed because of Claudius' reaction to the play that Hamlet had the actors perform.  After all, he's just been shown definitive proof, in his mind, that Claudius killed the king, Hamlet's father.  Imagine the hurt, anger, and feelings of betrayal that must be surging through Hamlet at this time.  Overall, I believe it was not evil that led Hamlet to act the way he did, I think it was emotion.  We see Hamlet, from the very beginning of the play, when Claudius and Gertrude both tell him essentially that he needs to get over his father's death and move on, that Hamlet is the kind of person who wears his emotions openly and is guided by them.  His love letters to Ophelia are also proof of how highly emotional Hamlet is. We see constant examples of how Hamlet is led by his emotions. I think the most "evil" act he commits is when he changes the letter that Rosencrantz and Guildenstern take to England so that they will be put to death.  I think that is a high price to pay for being pawns in Claudius' game.