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"You are in the wrong," replied the fiend; "and instead of threatening, I am content to reason with you. I am malicious because I am miserable. Am I not shunned and hated by all mankind? You, my creator, would tear me to pieces and triumph; remember that, and tell me why I should pity man more than he pities me? You would not call it murder if you could precipitate me into one of those ice-rifts and destroy my frame, the work of your own hands. Shall I respect man when he condemns me? Let him live with me in the interchange of kindness, and instead of injury I would bestow every benefit upon him with tears of gratitude at his acceptance. But that cannot be; the human senses are insurmountable barriers to our union. Yet mine shall not be the submission of abject slavery. I will revenge my injuries; if I cannot inspire love, I will cause fear, and chiefly towards you my archenemy, because my creator, do I swear inextinguishable hatred. Have a care; I will work at your destruction, nor finish until I desolate your heart, so that you shall curse the hour of your birth." (17.5)
The monster believes that a female companion is his only chance for happiness.
A fiendish rage animated him as he said this; his face was wrinkled into contortions too horrible for human eyes to behold; but presently he calmed himself and proceeded—(17.6)
The monster’s ugly appearance is equated with fiendishness.
"You must create a female for me with whom I can live in the interchange of those sympathies necessary for my being. This you alone can do, and I demand it of you as a right which you must not refuse to concede." (17.2)
"The interchange of those sympathies necessary for my being" is a roundabout way of saying, "I need someone to wish me good morning and yell at me for not taking out the trash." The monster wants someone to just be normal with.