Mary Shelley wrote Frankenstein as a [new] author heavily influenced by Romantic writers (Byron, Shelley—her husband, and Keats, as well as Wordsworth and Coleridge) whose focus deals a great deal with nature; e.g., Victor spends a great deal of time praising the landscape , and even the monster notices the beauty of nature when he hears birdsong.
There are many characteristics of Romantic writing, but a return to— and respect for—nature (e.g., Coleridge's somber epic poem The Rime of the Ancient Mariner) is a classic feature of Romanticism. The scientist would have been an unwelcome addition to the Romantics' world, as man began to look to what he could control and began to lose sight of what could and should be left to nature...and God.
In Frankenstein, Mary Shelley focuses on, among other things, the Industrial Revolution starting in the late 18th Century. Industry has taken off with technology (e.g., electricity), and machinery (e.g., cotton spinners). Science is garnering great interest; e.g., the Shelleys attended a lecture by Charles Darwin's grandfather, Erasmus, regarding biological evolution, something that would have been in the author's mind as she wrote. However, Shelley believes there is a danger in embracing these developments without proper vigilance.
Early fans of the Frankenstein were captivated with this cautionary tale...
...about the destructive power that can result when human creativity is unfettered by moral and social concerns.
seems to lean towards the idea that "man cannot completely control nature, and should not even attempt to". Instead, man should let nature take its course and not try to change the natural order of things.
Mary Shelley's Frankenstein becomes a warning (almost like a parable or lesson) to those who are too quick to embrace new sciences and technologies, as well as adopting a reversal of ethics and moral positions of that era (though the message is still relevant today).
Victor represents the scientist who, in the face of personal obsession, turns his back on what he knows is morally and ethically correct, and throws himself—without thought of consequence—into experiments to create new life, something no human should do. Victor sins against God also when he raids graveyards for body parts, disturbing consecrated ground. Victor loses sight of his place in the universe.
Shelley's warning provides examples of what happens when someone abandons caution and conscience: Victor builds a creature and abandons it, with no regard of his responsibility to either destroy it or teach it—or even see if this can be done. The creature's experiences are horrific: he is first rejected by his creator, and then by humanity—beaten and shot. He is alone in the world. With this negative "nurturing" the creature's "nature" becomes that of a monster—who believes he was made for love. In response to his experiences, the creature becomes a monster—a result of a scientist's desire to create new life—even though Victor's wish is philanthropic, his inanity causes the death of almost everyone he loves.
I have found over the years, that there is a paradox here: who is truly the monster, or are both "men" monsters?
The scientist (Victor) is an incautious, thoughtless, morally-shallow man who blindly pursues his scientific goals without thought to the ramifications of his actions on the rest of the world.