Eh, not so sure it's bad sci-fi, given that it's not far from historical norms.
Most of human history is a comparative handful of people executing effective control over most of the available resources, isolating themselves in heavily-barricaded encampments and putting lots of effort into maintaining that control (castles/cities/gated-and-guarded-communities/etc).
It's a pretty stable equilibrium: once you've got effective control over most of the available resources, you can easily afford to maintain your barricades, and if on the other hand everyone else is effectively shut out from those resources it's going to be pretty hard to organize much of a revolt; most of the shake-ups are due to sudden shifts in technology or unexpected "black swan" events (eg a mongol invasion or a plague).
The exact nature of the relationship between the barricaded and the rest varies with circumstance: sometimes the rest are useful for labor (like tilling the fields), or to raise an army; in the modern era it's often the case that the rest are left to fend for themselves, at least as long as they're not causing trouble.
You don't have to travel far to see the same pattern surviving into the present era: just go to Argentina, or Brazil, or Africa, etc.
So social organization resembling the dystopia in "Manna" has been more-or-less the normal human experience since Sumeria, if not earlier, and is still existent today for maybe 20-40% of the world's population (depending on where you draw your lines); it's possible that "western" modernity -- of the sort you have in the US/EU/Japan/Korea/ -- marks a turning point in history, but it could just be a brief interlude between variants-on-the-theme-of-feudalism, also.
On the face of it Manna is cartoonish and whatnot, but positing a return to quasi-feudalism is pretty much betting on mean reversion, which could be a bad bet but isn't necessarily comical.
Most of human history is a comparative handful of people executing effective control over most of the available resources, isolating themselves in heavily-barricaded encampments and putting lots of effort into maintaining that control (castles/cities/gated-and-guarded-communities/etc).
It's a pretty stable equilibrium: once you've got effective control over most of the available resources, you can easily afford to maintain your barricades, and if on the other hand everyone else is effectively shut out from those resources it's going to be pretty hard to organize much of a revolt; most of the shake-ups are due to sudden shifts in technology or unexpected "black swan" events (eg a mongol invasion or a plague).
The exact nature of the relationship between the barricaded and the rest varies with circumstance: sometimes the rest are useful for labor (like tilling the fields), or to raise an army; in the modern era it's often the case that the rest are left to fend for themselves, at least as long as they're not causing trouble.
You don't have to travel far to see the same pattern surviving into the present era: just go to Argentina, or Brazil, or Africa, etc.
So social organization resembling the dystopia in "Manna" has been more-or-less the normal human experience since Sumeria, if not earlier, and is still existent today for maybe 20-40% of the world's population (depending on where you draw your lines); it's possible that "western" modernity -- of the sort you have in the US/EU/Japan/Korea/ -- marks a turning point in history, but it could just be a brief interlude between variants-on-the-theme-of-feudalism, also.
On the face of it Manna is cartoonish and whatnot, but positing a return to quasi-feudalism is pretty much betting on mean reversion, which could be a bad bet but isn't necessarily comical.