One of the most fundamental differences between atheism and religion is that a religion is, by definition, a group of followers, while atheism is a collection of individuals. Each religion is built on some body of myths and rules that was compiled long ago and is now set in stone, inviolate. Membership in that religion is defined by obedience to these dogmas, which can be reinterpreted but not changed, neither to add nor to remove. No matter what new knowledge or moral advances emerge, religious believers are in a way trapped in the past, forever bound to uphold their creeds.
Atheism, however, has nothing comparable: no dogmas, no authority, no creeds to which every member must subscribe. Every atheist is free to discuss, criticize, or alter for themselves any belief held by any other, and even tenets held in common by many atheists can be revised or discarded entirely should it prove necessary. It is true in more than one sense that, to an atheist, nothing is sacred.
These two different worldviews can be likened to a cathedral and a garden. Religion is the cathedral, a vast and ancient edifice crusted with the baroque ornamentation of endless reinterpretations. At first glance it may seem grand, but at a closer look, one sees it for what it truly is: musty and stale with dogmatism, the altar ornate but sterile, the creeds carved in cold stone, the founders and saints now frozen in statue, their words as rigid and petrified as fossils.
In contrast, atheism is more like a wild garden. It is not rigidly structured like the cathedral, but its disorder is the exuberant disorder of life - a chaos of creativity, of free expression, a million bright blossoms each with its own voice and story to tell. And there is a hidden order beneath the seeming disorder, an invisible but strong thread of kinship that ultimately unites every tree and leaf and blade of grass. It endures not with the obstinacy of a stone block, something built to resist time, but with the constant rebirth of nature, made afresh each time some newly born freethinker discovers it for themselves.
The unchanging dogmatism of religion might be understandable if there was good reason to believe that it possessed the truth, since after all, the truth does not change with time. However, the evidence mitigates against that, and as a result the followers of religion are hobbled in many ways. Consider, for example, the area of morality. When it comes to deciding what is and is not moral, proponents of organized religion are trapped in this cathedral of the past, restricted by the collected beliefs of ancient people despite the fact that they live in a world those people could never have imagined. It is a strained fit at best, because books such as the Bible never mention a great many issues that are highly relevant today, and on the other hand, devote considerable space to a great many issues that are now utterly irrelevant.
The quintessential example is the way Christian fundamentalists wrestle with the Bible in an attempt to extract from it, via some exegetical alchemy, a verse forbidding abortion - a subject that, despite their efforts, that book never mentions at all, although it spends a great deal of space on far less important topics, such as how to deal with the "uncleanness" of menstruating women. (One wonders if these Christians do not, on some level, feel God could have made better use of his time.) On the other hand, the Bible clearly endorses human slavery on multiple occasions, forcing modern-day believers who now know this practice is thoroughly immoral to spend huge amounts of time and effort attempting to explain away these cruel and inhumane laws.
In contrast to all this, an atheist can live in the present, in the real world, with a head unclouded by the imaginings of the past. Atheists need not worry or obsess about what some long-dead tribal leader had to say when deciding our next course of action; nor do we feel any need to trawl through obscure texts in a vain search for guidance. We have the same gifts of reason and conscience as any other human being, including the ancient tribal leaders, and in addition we now possess much more understanding than they did. If we see that our current moral system is inadequate to deal with a new situation, we can conceive new principles to guide us, instead of trying to extract something relevant by twisting and squeezing what already exists. On the other hand, if a particular source says something that is immoral, we can simply acknowledge this and discard that source; we do not have to be endlessly making excuses for it.
Or consider the question of how we view the world - its origin, its extent, its fate, and the laws that govern it. Those theists who hold strictly to the cosmogony of their holy books are trapped in the small, limited imaginations of a bygone time. Earth was a small, simple place then, little more than a stage, where humans played their assigned roles under the eye of a God who would reward or punish them accordingly. The known world was, at best, a few hundred miles across, supported by pillars, girdled by uncrossable seas and mysterious wastelands populated by fierce alien tribes. Nature was mostly crowded out by the supernatural; the air was clouded with invisible hordes of angels and devils, spirits lurked in every hilltop and grove, and everything that happened was a miracle or an omen. Our lines of ancestry ran back only a few generations to the Garden of Eden, where humans were first sculpted out of animated dust, and our future looked ahead only a brief time to the world's fiery dissolution, which every single human generation has believed would occur in their own lifetimes.
We now know better, of course. The world is a far more immense, complex and majestic place than these ancient authors realized, stranger and yet more wonderful. Regardless of their literary merit, these stories fall short; they do not do justice to the reality. But dogmas do not change, and as a result religious believers are trapped with these small myths, either allegorizing them to the point of meaninglessness, or worse, continuing to defend them as if they represented truth. Atheists have no such restrictions, however, and in the light of reason these myths evaporate, allowing us to perceive the greater truths that lie above them. In the light of reason, the Genesis story and other cosmogonies come tumbling down, like a painted backdrop, to reveal the unimaginably vaster and more beautiful story of the cosmos, and the firmament covering the world shatters to reveal endless blue sky and the starry arc of the galactic plane beyond. The faded scripts the religious read from cause them to overlook the much greater story weaving all around them and through them, a multi-dimensional helix of history and time encompassing everything from the vast migrations of human history to each base pair of our DNA, but an atheist can set aside these scripts and draw from the true, much more magnificent, book of nature.
There is grandeur in this view of life, a clarity and power that is all the more awe-inspiring because it is not all about us. We are but one small piece of a vast story, one brilliant bloom in a beautiful and wild garden, one voice in a cosmic fugue. Our investigations into the nature of things have revealed to us a vision that far surpasses the small and inadequate myths of the past, and one an atheist can accept without reservation, unhampered by artificial preconceptions of the way things should be.
Though fantasy has its place in human existence, spending your whole life inside one fantasy, one imagination, is to miss out on all the most wonderful things reality has to offer. The sheer joy and freedom of leaving these myths behind, using one's own mind to study and judge, is something that can only be imagined by those trapped inside literalist interpretations of ancient religious dogma. To these people, I say: leave the cathedral, step out into the sunshine, and take a walk in the garden. You may like what you find.