Atheism is a religion like "off" is a TV channel.
Atheism is a religion like bald is a hairstyle.
Atheism is a religion like abstinence is a sex position.
My personal favorite analogy, which I remember reading a long time ago on Usenet, said that calling atheism a religion was like saying the following:
You don't have tuberculosis, which means that you have non-tuberculosis, a form of tuberculosis.
I'll admit that I get in a bit of a huff when I hear that atheism is a religion, and those things spring to mind. For me, I find it hilariously ironic when a religious person says it in an insulting way. "You're criticizing religion? Well, you're in a religion too!" Seriously? Your best defense essentially admits that there's something wrong with your position when you accuse the other person of doing the same thing.
Anyway, now that we've covered the standard responses, let's see if I can come up with some original thoughts and unpack this notion that atheism is a religion. First off, I will fully admit that atheists can be just as prone to tribalism as any other group of people. But is tribalism necessarily the same as religion? People can be tribalistic about sports teams, but are we going to say that being a fan of a sports team is the same thing as being religious? I'm not quite willing to go there, and I imagine that both atheist and religious sports fans aren't likely to want to equivocate like that.
I think that my issue with calling atheism a religion stems more from me being a fan of clear language than being an atheist. I've already written a blog post about what atheism is and what it isn't, but in a nutshell, all atheism reveals is how a person feels about whether there is a god or not. There just isn't much to it, if you think about it. There are atheists who believe in ghosts. There are atheists who are skeptics. There are atheists who are humanists. There are atheists who are nihilists. In other words, it's too narrow of a criteria to even call it a belief system, much less a religion.
Part of the problem no doubt comes from the notion that most people in the West automatically associate the question of a god's existence with religion. There seems to be this false assumption that religions all deal with that question, but there are religions that don't give much thought to it at all, and there are some that are completely atheistic, including Taoism, Confucianism, and some forms of Buddhism. You also have some Jews who practice all the religious rituals yet are technically atheists.
Let's take just atheistic Buddhism as an example. If atheism is a religion, then what is their religion? Is it atheism or is it Buddhism? Sounds like kind of a silly question, doesn't it? I'd reckon that most of us would say that Buddhism is the religion and atheism is just one aspect of the religion.
And if atheism is a religion, then does that make theism a religion? I know plenty of people who believe in a god of some sort, but I wouldn't say that suddenly makes them members of a religion or even religious - especially when they don't engage in any rituals or subscribe to any sort of divinely revealed moral code. If you're going to say that atheism is a religion, then it makes just as much sense to say that theism is one as well, but I have a hard time believing that anybody is going to make that particular argument.
Lastly, the part that doesn't sit right with me is that it's kinda like saying that you're going to be part of a religion no matter what. You believe that God came down in the form of man and died for your sins and you need to confess them in order to be saved? You're religious. You don't believe that? You're religious too. What?
Ultimately, my problem is that by simply calling atheism a religion essentially makes the word "religion" pretty useless. I realize that there's some debate as to what might qualify as a religion. There are adherents to beliefs like Confucianism and Humanism who will argue that they're better classified as philosophies rather than religions, and honestly, I kinda side with them. I could probably do a whole blog post on that alone. But the point is that religions usually offer a set of beliefs, not just one. Also, they often involve rituals, authority figures, and revealed knowledge. Many of them also have special days that require special observances.
The simple act of not believing in any of the various gods that have been proposed being a religion? It doesn't include any of those trappings, and I just can't see my way to that conclusion.