If this play were called Laertes and all the scholars spent years analyzing his actions and his lines, this moment would be much analyzed. It might be Laertes’ tragic flaw. People like to say that Hamlet’s flaw is his inaction (a questionable, though much repeated thesis) but Laertes’ flaw might well be his gullibility, his willingness to be a pawn in Claudius’ game. His impetuousness gets him into the throne room and into his sister’s grave with Hamlet – but it is his susceptibility to be manipulated that REALLY gets him killed.