Do you mean the monster's argument for wanting to kill Frankenstein or Frankenstein's argument for wanting to kill the creature he created? Since I am not sure, I will answer both.
Frankenstein dies aboard Walton's ship, having failed to kill the monster. He finally came to the conclusion that he must destroy his creation for the good of his fellow beings. This is also why he refused to create another monster as a companion for the monster - it would have done more harm to his fellow human beings, in his mind. Before his death, he asks Walton to pursue and kill the monster, however, because he fears that the monster will go on killing. He fears that because the monster is still miserable because of being lonely and loathesome, he will continue to seek vengeance against humans because it was a human who created him.
When Frankenstein dies, the monster comes on board the ship and hovers over his dead creator, bemoaning the fact that Frankenstein is now dead. The monster states that Frankenstein is, in reality, another one of his victims because in killing everyone that Frankenstein loved, the monster has caused Frankenstein's own death, through grief. Walton chastises the monster, telling him that his supposed grief is worthless because if he had listened "to the voice of conscience and heeded the stings of remorse before you had urged your diabolical vengeance to this extremity, Frankenstein would yet have lived." The monster defends himself. He tells Walton that Frankenstein has not suffered as much as he has suffered. "Do you think that the groans of Clerval were music to my hears?" He tells Walton that it hurt him to have to kill all of Frankenstein's friends and loved ones, because they were innocents, and it was Frankenstein who was guilty. The monster explains that even after he killed Clerval, Frankenstein was still planning on getting married, seeking hapiness for himself, while he, the monster, was still miserable and without a companion. He claims that Frankenstein was selfish and thought only of himself, of his own happiness. The monster accuses Frankenstein of being a hypocrite and blames Frankenstein for turning him (the monster) into a loathesome being. He tells Walton that Walton has only heard Frankenstein's side of the story and that he, the monster, has suffered far more than Frankenstein. "Am I to be thought the only criminal, when all humankind sinned against me?"
I agree with the monster. Each time I read this novel again or have to teach it, I feel the same way. Frankenstein never did enough to stop the killings, in my view. He should have put the monster out of his misery long ago. He tries to go to the authorities once, but when they blow him off, he gives up, and then more people are killed. Also, he could have tried to create a companion for the monster because the monster told him that if he had a companion, he would leave Frankenstein and his family alone. I don't like Frankenstein very much, so yes, I would agree with the monster. I think Frankenstein is selfish and weak.
Others may have different views, and you can see what YOU think.