After reading you notice that the creature, after committing murderous violence, is not a bad person at heart. The one responsible for all this is Dr. Victor Frankenstein. When Victor first creates the monster he is surprised with "breathless horror and disgust" (page 35) when he first sees it. So he abandons it, not caring about its safety. This is like giving birth to a baby, then leaving it in the woods to fend for itself. The creature becomes nothing more than a "poor, helpless, miserable wretch" (page 71), living on a diet of berries and acorns, and feeling
"Frightened and desolate" (page 71). He learns to talk and read watching a small family for a couple years, and wants their company so that they can be "sympathizing with [his] feelings and cheering [his] gloom" (page 93). But every time he interacts with the humans they are scared are beat him. But when he rescues a young girl from drowning in a river, he is not thanked. He is shot. He just saved someone’s life, showing he has a heart, therefore deserves some sympathy. So of course the monster is going to think, no matter what he does people will never accept him and always neglect and treat him poorly. He murders William Frankenstein because he is a relative of Victor, and frames Justine because he knows she will never be sympathetic towards him, since she is a member of the human race (talk about being in the wrong place at the wrong time).
When the monster finally gets a chance to speak with his creator, he asks for one thing! A creation, of the opposite sex. Victor says yes at first, but decides that it will be too risky to create another being which might be "ten thousand times more malignant than her mate" (page 120). So he eventually destroys the second creature. Leaving the first monster once again, alone. At this