Laertes' motivation is honorable. He is trying to punish his father's killer. However, Laertes is also naive and does not realize he is really being manipulated by Claudius in Claudius' desire to see Hamlet dead. As the play progresses, Laertes seems genuinely touched by Hamlet's request at forgiveness and even tells Claudius that to kill Hamlet is "almost against my conscience". Once Laertes discovers the "villany" of Claudius, he quickly tells Hamlet and asks to exchange forgiveness with him. Thus, Laertes has acted as an unwilling pawn of Claudius, but is quick to reveal the plot once he sees the true motivation behind Claudius' actions. I think that's about as honorable as one can get.