Based on the religion etymology, the meaning of the word has changed in multiple ways that definitions now abound and are incoherent. Some entities considered a religion in one definition is excluded in another. This incoherence is due to the fact that the concept religion involves both an aspect of society and the structure of human subjectivity (See The true, the beautiful, and the good).
Because of the incoherent way the concept of religion is used today, we need to establish whether it even has an essence. In addition, because the concept of religion arose from a specific place and time, changed throughout history, and used to discriminate other cultures, we need to establish whether it even corresponds to something real in the universe or should we just stop using it.
References
Schilbrack, K. (2022). The Concept of Religion. In E. N. Zalta (Ed.), The Stanford Encyclopedia of Philosophy (Summer 2022). Metaphysics Research Lab, Stanford University. https://plato.stanford.edu/archives/sum2022/entries/concept-religion/
over time, the extension of the concept has evolved in different directions, to the point that it threatens incoherence.
Many have complained that arguments about how religion should be defined seem unresolvable. To a great extent, however, this is because these arguments have not simply been about a particular aspect of society but rather have served as proxy in a debate about the structure of human subjectivity.
First, the disparate variety of practices now said to fall within this category raises a question of whether one can understand this social taxon in terms of necessary and sufficient properties or whether instead one should instead treat it as a family resemblance concept. Here, the question is whether the concept religion can be said to have an essence.
Second, the recognition that the concept has shifted its meanings, that it arose at a particular time and place but was unknown elsewhere, and that it has so often been used to denigrate certain cultures, raises the question whether the concept corresponds to any kind of entity in the world at all or whether, instead, it is simply a rhetorical device that should be retired.
A concept used for scrupulous devotion was retooled to refer to a particular type of social practice. But the question—what type?—is now convoluted. The cosmic version of the concept is broader than the polytheistic version, which is in turn broader than the theistic version, and the functional definitions shift the sense of the term into a completely different register. What is counted as religion by one definition is often not counted by others.