Atheism is not a religion, but that does not mean that some atheists are not religious. In fact, we now have at least one atheistic religion. To understand how this is possible, it is helpful to remember what atheism is and what it is not. Atheism refers to the lack of belief in gods, meaning that atheists are people who do not believe in gods. There is nothing in the definition of atheism that prevents people from believing in souls, unicorns, angels, fairies, demons, aliens, Bigfoot creatures, or all sorts of other entities that most skeptics would reject. Similarly, there is nothing in the definition of atheism that would prevent atheists from being "spiritual" or even believing in some form of life-after-death.
Nontheistic religions are nothing new. Some people will tell you that certain forms of Hinduism, Buddhism, Jainism, and various neopagan traditions are nontheistic. And of course, most contemporary forms of Satanism are nontheistic in that their adherents do not believe in any gods and do not worship a literal Satan. There is nothing about atheism, then, that would prevent an atheist from joining a nontheistic religion if he or she was inclined to do so.
This brings us to an important point about atheism: atheism is distinct from anti-theism. Many atheists are also anti-theists (i.e., people who oppose religion); however, this is not true for all atheists. Some atheists, in fact, appreciate a great deal about religion even though they do not believe in gods. Some of them do end up joining nontheistic religions, making them religious atheists.
Some of us scratch our heads and ponder, "Why would an atheist want to join a religion?" It is helpful to remember that not all religions are theistic and that not all atheists are hostile to religion. Just because you or I might not want to be part of a religion does not mean that other atheists don't. And just because they are atheists does not mean they can't.
But why can't atheism be a religion? If there are nontheistic religions, why can't we consider atheism one of them? These are good questions, but they have an easy answer. Atheism cannot be a religion because it does not involve any sort of belief system. Atheism is nothing more than a lack of belief in gods. Without a shared belief system of some sort, it does not qualify as a religion.
Consider the newest atheistic religion, The Satanic Temple, as an example. They have seven fundamental tenets in which their members believe. In fact, they require anyone who wants to join them to express their support for these tenets. Atheism does not have anything like that. Additionally, atheism does not have a central organization, physical location, or means of joining. There are organizations like American Atheists, and I suppose they could explore the possibility of gaining designation as a religion from the IRS, but they have not done so yet.
But aren't those Satanic Temple folks really just trolls? I mean, aren't they merely pretending to be a religion in order to stick it to Christians? Probably. I don't think that makes what they are doing (e.g., working to preserve the separation of church and state) any less valuable. And if Scientology gets to reap the tax benefits associated with being a religion, why not Satanists and other atheists?
