Like a cockroach, propaganda can survive. That category includes some of the undying arguments against materialistic naturalism. As I've said previously here and here, I define materialistic naturalism as a philosophical stance that contains two overlapping statements. First, if anything supernatural exists, then it is as equally indetectable and irrelevant as if it's nonexistent. Second, anything that does exist originates in material/physical stuff. I write "stance" because I recognize that these sweeping propositions aren't exhaustively proven like facts. Rather, the propositions match known facts and additionally presume that unknown facts will match just as closely.
Today's propaganda cockroach is the argument that materialistic naturalism enforces a total loss of human significance. It sounds like, "Without supernatural entities or metaphysical factors, nothing grants humans greater significance than anything else. Since a single atom cannot be significant, humans composed solely of atoms cannot be significant. Since significance is bestowed by a qualified external judge, humans cannot be bestowed with significance in the absence of supernatural entities. Since something must be relatively central and influential in the universe in order to be significant, humans cannot be significant unless physical laws assign those exceptional qualities to humans. Since something must be relatively long-lived or imperishable in order to be significant, the material of mortal human lives cannot be significant whenever the scale of the universe is considered massively old by comparison. Since significance is often an intangible feeling, tangible things cannot be the sole background of significance." And so on.
Although this overcomplicated line of reasoning might have enticed me once, I have less patience now for the "question" of human significance in materialistic naturalism. In my current perspective, its answer verges on "trivial", similar to the simplistic trivial solutions of a mathematical problem or proof. For instance, the subsets of set Q are the sets only of members that are also members of Q. The problem of finding the subsets of Q that fit particular criteria can be...hard sometimes (in fact, theoretically proven to not presently have a uniformly feasible general solution). But Q is a trivial subset of Q; after all, Q is a set of only members that are "also" members of Q.
Essentially, the trivial pragmatic reason behind the greater significance of the tiny materials within humans is that the materials are within humans. And the trivial reason humans are so significant to us is because we're human. My head is significant to me because it's my head. My brain is significant to me because it's my brain in my head. My brain cells are significant to me because my brain cells are in my brain in my head. Comparable "logic" applies to humans other than me. Their brain cells are significant to me because their brain cells are in their brains in their heads. Certainly I would acknowledge the awful significance of their tiny brain cells functioning worse, perhaps due to a degenerative disease.
Furthermore, this trivial definition of human significance isn't in conflict with the finite realities of the small space-time position and impact of human lives. It's not hampered by confinement to a single off-center planet in a single off-center solar system in a single off-center galaxy. Nor is it hampered by the limited number of decades between birth and death. The more insightful question isn't whether grander knowledge of the whole universe reduces significance. It's "Why would anyone think it reduces significance?" Why was there such a staggeringly disproportionate estimate of significance to start with? If significance to the whole universe shrinks as the estimate grows more accurate, then nothing is "lost" except the former believability of the outlandish fictional estimate. Humans have only been "demoted" from a noble rank that was never theirs in actuality anyway. How shocking it is to not assume that humans aren't the pinnacle or purpose of the whole universe.
Even so, I can appreciate one of the possible motives for seeking to expand significance and anchor it firmly in external realities: objectivity. I admit that the opposite strategy is more subjective in nature. If significance is derived from human judgment, then it's probably bounded correspondingly by provincial human concerns. And given the multitude of humans and human concerns, it will probably be constructed in a multitude of varieties. But the quest for objective significance is fruitless. Perfectly objective significance would be somewhat detached from human standards. Yet if significance were somewhat detached from human standards, then humans wouldn't be likely satisfied with it. Just as one human's measurement of significance might not be satisfying to another, neither might an inhuman measurement of significance. To name the obvious example, someone might reasonably disagree with "objective divine writ" which calls them a negligible member of a permanently insignificant out-group...
In contrast, I don't understand a second possible motive for rejecting materialistic naturalism: the absurd poetic demand that a thing's explanation must have identical human significance as the thing itself. Depending on the context and goal, either the thing or the explanation might have more applicable significance. The activity of reading about the Krebs cycle shouldn't need to feel energetic for the information to be acceptable. Memorization of the chemical bonds of serotonin doesn't need to alleviate depression. The numerical magnitude of the neuron threshold potential doesn't need to trigger memories of Grandmother. Accurate representations of low-level complex realities don't somehow invalidate or replace the significance of human-level experiences. The explanation's significance is independent. Its amount of "mystery" isn't vital to preserving the experience's significance. Detailed studies, consistent with materialistic naturalism, don't diminish it. Likewise, shadowy conjectures, inconsistent with materialistic naturalism, merely decorate it. A decisive event in someone's personal history affected them vividly and had long-lasting ramifications. That's why they weighed its significance so heavily, no matter the alleged comparative contributions of natural processes or ineffable Fate, no matter the individual's vocation of scientist or clergy.
That objection is related to the mistaken assertion that someone who follows materialistic naturalism cannot claim that human significance is an important question. I don't wish to give that impression. I would never state that the question's trivial difficulty is accompanied by trivial importance. Identifying precise manifestations of human significance is a valuable undertaking. I think it's commendable to deliberately evaluate one's own wide-ranging effects, not from an unearthly vantage point, but through reference to one's own powers and chosen ideals. Why is a chosen ideal a worthy benchmark of significance? The answer is trivially obtained: it's worthy by whatever rationales that caused it to be chosen, of course. It's meaningful via straightforward ties to the realities of specific human experiences. It's not dependent on stupendous otherworldly significance, grounded in mystical afterlives and deities. Why does it need to be? Why isn't it enough?