It is in Chapter Seventeen that the creature argues for the creation of another being, like himself, so that he can have company in his position of being an outcast of humanity. He has discovered through his adventures, and in particular with the De Lacey family, that he is an outcast in every sense of the word, unable to joy friendship or love with man, yet at the same time he has been created so as to desire these things. Therefore, to his mind, it only seems logical that he should have someone like himself, who will not be scared away by his appearance, who can satisfy those desires inside of him. This would in turn cause his hatred of mankind and of his creator to cease as he would be able to have his needs met. Note what he says to Victor in Chapter Seventeen:
"I swear to you, by the earth which I inhabit and by you that made me, that with the companion you bestow I will leae the neighbourhood of man and dwell as it may chance in the most savage of places. My evil passions will have fled, for I shall meet with sympathy!"
Sympathy, which is what the creature has not yet encountered (except for the blind Mr. De Lacey), is what he feels will act as an antidote to his hatred of humanity and cause him to dispense with his violence.