My central claim: Fallen World theodicy offers no criterion for what counts as a consequence of the fall, which makes it unfalsifiable, and which licenses absurd extensions. Even if I were a theist, I would still find it vacuous as it explains everything and nothing at once about how the world is in its current state.
Allow me to give the conclusion that I hope to support: A believer in the Fallen World theodicy can, and perhaps even must, believe that feces smells unpleasant only because sin entered the world. I say this because Fallen World theodicy is the oft used scapegoat to explain all natural suffering like cancer and tsunamis, but the implications of this claim must be grappled with, and would lead to the above conclusion for the believer in question.
Argument 1: Unevidenced and Unfalsifiable
Unless you don't believe in the scientific consensus of an old earth and evolution, the fact is that natural suffering and their causes have been in existence long before humans could ever walk the earth and do whatever it is that caused the fall. Attempts to account for this can go as far as to claim that the world was actually a paradise with no disease or natural disasters, but when humans introduced sin, then the world was retroactively changed by some temporal means to then be full of disease and suffering before humans came about. Of course, this is neither falsifiable nor evidenced in any way whatsoever. It is pure wild speculation at best.
Less popular is the suggestion that it's actually only humans that were immune to disease and natural suffering when they first came about, but when sin came, that's when this immunity vanished. Again, lacking evidence. There is no way to know this is true beyond mere speculation. It suggests that the earliest human ancestors, somewhere within the delineation between homo heidelbergensis and homo sapien, were just immune to disease and natural disasters for some period, and then this immunity ended somehow.
Argument 2: No Epistemic Limits
Christians who abide by the fallen world theodicy will sometimes claim that things like cancer or tsunamis or earthquakes were not meant to be part of our universe. They were not in the initial blueprints of God's design, they say, and they do so despite having no real confirmation of what the pre-Fallen world actually was like. Ideas about the pre-Fallen world are extrapolations at best.
The issue comes about when there is no real epistemic limit to what could ever actually be excused as part of a fallen world. It can be something as terrible as a tsunami that kills thousands, or as small as an itch on the nose. There is no identifiable or consistent mechanism that translates whatever state the universe was in prior to the fall of man to the state it's in now.
Before the fall of man, cancer didn't exist. After it, now it does. How? Did sin introduce carcinogens? What about earthquakes? Were there none before, and now there are? How? Did sin introduce tectonic shifts? Did those not exist before sin entered the world? We don't have any real explanation for how this occurs. All we have is a broad encompassing category of bad things, and they must all not have been bad or not have existed at all before the fall, regardless of how fundamentally different the causes are of each example. Sin just can just cause all manner of reality-bending that introduces suffering into the world, from cancer to plague to dengue fever to predation to parasites to sudden infant death syndrome, etc.
But because there's no epistemic limit to these speculations, we can include even minor inconveniences or limits to human ability, can we not?. Take my earlier example with feces: sure, it has its uses, but it smells unpleasant. Well, if we can just say anything about the Fallen World without needing to back it up, then we can claim that feces actually smelled delightful before the Fall. Hell, why not take it a step further, and say that outright eating feces was nutritious, but sin made it unpleasant and poisonous?
And why stop there? Maybe the unpleasant feeling when a person eats too much food is also a result of the fall. Maybe the fact that we are constrained by gravity is also a result of the fall. Maybe children physically and mentally matured quickly rather than undergo awkward transition periods into adulthood before the fall. Virtually any undesirable or inconvenient aspect of our world can be declared as a consequence of the fall after the fact. Who is the believer to say otherwise, when there is no epistemic standard to deny it with?
Conclusion:
The Fallen Word theodicy, the way it's used so often, recognizes a fact of our world: "There exists natural suffering not caused by human decisions." And in acknowledging this, it tries to answer the question: "How can this happen with a tri-omni god?"
It answers with statements without evidence, blanketly placing any and every kind of natural pain or inconvenience into one whole category, and putting it squarely on the shoulders of humans rather than on the all-knowing designer. It is a means of salvaging God's tri-omni properties by asking "How can we explain natural suffering to be NOT the fault of the all-knowing and all-powerful designer of the universe?" There is no limit to what it can excuse because Fallen World theodicy is clearly not meant to mechanistically explain the state of the world. I'd argue that its purpose is an ad hoc shift of the blame from God to man. This is why I say that the believer must accept the idea that bad smells are a result of the fall, because if they can simply make unevidenced statements as to the pre-fall state, then any claim is as good as any other as long as it falls under the category of naturally occurring unpleasantness. One can claim that God made humans could literally eat poop without a problem prior to the Fall, and the believer in the Fallen World couldn't possibly say otherwise, or else open the door to skepticism and a need for evidence for each claim.
Note: At the least, I can acknowledge that other arguments that explain the state of the world ("God puts these sources of natural suffering as a test", "Natural suffering leads to greater goods", "Natural suffering builds virtues", etc.) avoid the issues I stated to some extent. They at least show that these sources of natural suffering were purpose-built rather than a sudden accidental state inexplicably brought about by human beings.