The word “religion” is a label for a category. That may seem like an excessively obvious statement, but it has implications that get missed surprisingly often. Categories are not, by and large, things that exist out there in the world. They’re abstractions—linguistically, culturally, and contextually specific abstractions—that human minds use to sort out the disorder and diversity of experience into some kind of meaningful order. To define a category is simply to draw a mental boundary around certain things, as a way of stressing their similarities to one another and their differences from other things. To make the same point in a slightly different way, categories are tools, and a tool, as a tool, can’t be true or false; it can only be more or less useful for a given job, and slight variations in a given tool can be useful to help it do that job more effectively.
A lack of attention to this detail has caused any number of squabbles, ranging from the absurd to the profound. Thus, for example, when the International Astronomical Union announced a few years back that Pluto had been reclassified from a planet to a dwarf planet, some of the protests that were splashed across the internet made it sound as though astronomers had aimed a death ray at the solar system’s former ninth planet and blasted it out of the heavens. Now of course they did nothing of the kind; they were simply following a precedent set back in the 1850s, when the asteroid Ceres, originally classified as a planet on its discovery in 1801, was stripped of that title once other objects like it were spotted.
Pluto, as it turned out, was simply the first object in the Kuiper Belt to be sighted and named, just as Ceres was the first object in the asteroid belt to be sighted and named. The later discoveries of Eris, Haumea, Sedna, and other Pluto-like objects out in the snowball-rich suburbs of the solar system convinced the IAU that assigning Pluto to a different category made more sense than keeping it in its former place on the roster of planets. The change in category didn’t affect Pluto at all; it simply provided a slightly more useful way of sorting out the diverse family of objects circling the Sun.
A similar shift, though in the other direction, took place in the sociology of religions in 1967, with the publication of Robert Bellah’s paper “Civil Religion in America.” Before that time, most definitions of religion had presupposed that something could be assigned to that category only if it involved belief in at least one deity. Challenging this notion, Bellah pointed out the existence of a class of widely accepted belief systems that had all the hallmarks of religion except such a belief. Borrowing a turn of phrase from Rousseau, he called these “civil religions,” and the example central to his paper was the system of beliefs that had grown up around the ideas and institutions of American political life.
The civil religion of Americanism, Bellah showed, could be compared point for point with the popular theistic religions in American life, and the comparison made sense of features no previous analysis quite managed to interpret convincingly. Americanism had its own sacred scriptures, such as the Declaration of Independence; its own saints and martyrs, such as Abraham Lincoln; its own formal rites—the Pledge of Allegiance, for example, fills exactly the same role in Americanism that the Lord’s Prayer does in most forms of Christianity popular in the United States—and so on straight down the list of religious institutions. Furthermore, and most crucially, the core beliefs of Americanism were seen by most Americans as self-evidently good and true, and as standards by which other claims of goodness and truth could and should be measured: in a word, as sacred.
I'll just assume that genuine Druid priests were wiser.