... A human being in perfection ought to always pursue a calm and peaceful mind, and never to allow passion or a transitory desire to disturb his tranquility. I do not think that the pursuit of knowledge is an exception to this rule. If the study to which you apply yourself has a tendency to weaken your affections and to destroy your taste for those simply pleasures in which no alloy can possibly mix, then that study is certainly unlawful, that is to say: not befitting the human mind. If this rule were always observed, if no man allowed any pursuit whatsoever to interfere with the tranquility of his domestic affections, Greece had not been enslaved; Caeser would have spared his country; America would have been discovered more gradually; and the empires of Mexico and Peru would not have been destroyed.
I think this passage is extremely revealing to the point that it complicates the typical reading of the novel as exclusively "a parable about the dangers of technoscience gone astray," as Prof. Johns summed up in his original post. I think the issue that Shelley is bringing to us is more specific, namely a theory of human nature that places the human race's faculties as a social animal before all else.
At the end of the passage, Frankenstein claims that interference with the "domestic affections" (familial love and community) of man, through obsession, greed, or other consuming distraction, has led to a great number of the major catastrophes throughout history. (It is actually quite a progressive bit of stealth anti-imperialism that Shelley considers the rapid 'discovery' and conquest of North and South America among such great classical calamities as the fall of Rome and Greece, and grammatically implies that their destruction came from without rather than within as with Caesar). But obviously it is that Frankenstein's downfall has a modern character: it comes about through the rationalist individualism of his day; his attempt at conquest of the natural world is scientific rather than imperial. I think Shelley's placement of the rationalist / individualist man of the post-Enlightenment world within the history of human folly and downfall is quite radical. With this passage, I think, she presaged many of the developments of hyper-individualism and advanced capitalism we would go on to see in the 20th and 21st centuries, even while placing them within a continuum of human failures which express themselves in new combinations as material conditions in society develop.
If we expand its scope from a son's separation from his family to the relationship between individuals in society as a whole, we could easily see the paragraph above as an indictment of the modern suburb which physically distances neighbors from one another, replaces family bonding with internet, television, and videogames, nullifies community and interdependence by requiring car travel to big box grocery stores, etc. in pursuit of personal wealth, perpetual entertainment, and a hollow "American Dream." This reading, it seems, has a great deal more modern resonance than simply the generic idea that technology, generally, may be bad for us if we happen to broadly go "too far," however far that might be. Rather than just saying "watch out" and leaving us to wonder what we're watching out for, Shelley is giving us a specific problem and a solution.
I think that this view of the novel gives a more meaningful role to the monster, as well.. The monster is created at the height of Frankenstein's obsessive solitude, and only appears to him definitively once more when he is again totally alone in the dizzying landscape of the winter mountains. It is, truly, the child of Frankenstein's self-obsession, and through its own story we realize the horror of its predicament: it is absolutely alone in its uniqueness, without any fellow creatures with which it can connect or relate. It stands alone, outside of and rejected from the human community, though in watching the family at the cottage it desires and attempts (and ultimately fails) to enter it.
This is the real tragedy that Shelley seems to be warning us against: that the children of modernism may find themselves entirely without a place within any human community, severed entirely from their nature as social beings. If we continue thinking about suburbs as emblematic of this loss in our era, could we think of, perhaps, the Columbine shooters, or any of the office or school rampages throughout the 90s, as the "Frankenstein's monsters" of post-Enlightenment individuality as produced within advanced American capitalism? The murders they committed strangely reflect the monster's murder of William, acts of misdirected, amoral rage intended against the creator responsible for their alienation.
The traditional reading of the novel as a vague parable against scientific inquiry in general seems altogether too limited in this light, and I think it deserves a close look as a grand critique of post-Enlightenment modernism and its creation of an atomized, disconnected individual.