There are a number of reasons why it was not correct for the creation of a monster. Let me give you a few of these reasons.
First, Victor Frankenstein played the role of God. He thought he could tamper with knowledge and create life without thinking about what he was doing on a deeper level. There is a strong undercurrent of the evils of pride and hubris.
Second, Victor Frankenstein did not consider the ramifications of creating a new life. Would he accept his creation? How would the world consider this new creation? The alienation that this monster feels is real and it is due to the lack of foresight by Victor.
Third, Frankenstein did not consider the feelings, desires, and wants of the monster that he created. He was not willing to take any responsibility for his creation.