At its heart, Mary Shelley's Frankenstein is interested in the question of nature vs. nurture: are people blank slates that are formed by experiences and environment, or are we born with certain...
At its heart, Mary Shelley's Frankenstein is interested in the question of nature vs. nurture: are people blank slates that are formed by experiences and environment, or are we born with certain traits—like being evil? What does the book seem to suggest? How do you know?
Frankenstein suggests that our experiences and environment determine what we become.
The monster is the best example of this, of course, because he goes from being a rather innocent being to a murderer. From his very first instances of knowing movement and action, he merely goes up to Victor and smiles.
. . . I beheld the wretch—the miserable monster whom I had created. He held up the curtain of the bed; and his eyes, if eyes they may be called, were fixed on me. His jaws opened, and he muttered some inarticulate sounds, while a grin wrinkled his cheeks.
The monster obviously has no ill intentions toward Victor. As well, later on in the novel, the monster actively tries to get to know people and to somehow be what they might want him to be.
People scatter and scream at just the sight of the monster. The monster only ever wanted to have companions and to escape loneliness. He goes to great lengths to get people to like him, even attempting a convoluted plan to educate himself and then befriend a blind man. The entire plan fails and that starts the monster on his path to being a murderer. Even so, he continued to do good things for others despite having been scorned once more in his attempt to befriend a blind man.
I rushed from my hiding-place; and, with extreme labour from the force of the current, saved her, and dragged her to shore. She was senseless; and I endeavoured by every means in my power to restore animation, when I was suddenly interrupted by the approach of a rustic, who was probably the person from whom she had playfully fled. On seeing me, he darted towards me, and tearing the girl from my arms, hastened towards the deeper parts of the wood. I followed speedily, I hardly knew why; but when the man saw me draw near, he aimed a gun, which he carried, at my body, and fired. I sunk to the ground, and my injurer, with increased swiftness, escaped into the wood.
However, after this incident of being injured in return for saving a young girl, his heart hardened and he, "vowed eternal hatred and vengeance to all mankind." He never wanted to hate humankind and had always done everything he could to gain the friendship of humans. The monster was never driven to commit acts of violence or revenge before he had been so harshly scared, emotionally and physically, that his internal moral compass broke.
Even after murdering Victor's younger brother, William, the monster does not want to outright kill Victor. The monster simply asks Victor to make him a companion so he will never be lonely and can happily live in the wilderness away from human settlements.
The monster never wanted to kill others but was led to when faced with the hatred of everyone, including his creator, and the prospect of being alone forever.