To save readers the suspense, no, atheism is not a religion. Atheists can have political quasi-religions (like Communism) or some other type of fanatically held dogmatic beliefs, but simply being atheist doesn’t indicate whether those types of beliefs are or aren’t present.
Like any honest approach to the conversation, we should define terms first, in the most reasonable way we can. What does religion or religious actually mean and refer to.
Wordnick.com reporting the American Heritage Dictionary of the English Language defines religion:
1. “The belief in and reverence for a supernatural power or powers, regarded as creating and governing the universe.”
2. “A particular variety of such belief, especially when organized into a system of doctrine and practice.”
3. “A set of beliefs, values, and practices based on the teachings of a spiritual leader.”
The Oxford English Dictionary definition for religion:
“A state of life bound by religious vows; the condition of belonging to a religious order.”
“Etymology… Anglo-Norman and Old French, Middle French religion (French religion ) system of beliefs and practices based on belief in, or acknowledgement of, some superhuman power or powers, also any particular such system.”
“Religion, human beings’ relation to that which they regard as holy, sacred, absolute, spiritual, divine, or worthy of especial reverence. It is also commonly regarded as consisting of the way people deal with ultimate concerns about their lives and their fate after death.”
So let us connect the common threads in all these definitions to form a working definition of our own. Religion involves a system of beliefs, as opposed to fleeting hypotheses and philosophical musings. It includes holding sincerely-held beliefs in the existence of the supernatural. And this system of beliefs about the supernatural are considered sacred and often inviolable (immune to criticism).
The elephant in the room is that belief systems like Communism would not qualify as a religion in the strict sense. But one could consider it quasi-religious in that it is a system of beliefs, it has what is nearly considered a prophet (Marx), and the teachings are often dogmatically held to as unassailable. I’m using Communism as an example, but this works with any similar political or ideological religion. I don’t know who the prophet of Anarcho-Capitalism is (maybe Ayn Rand?), but adherents of it often come across as religiously dogmatic in their belief system, just like Communists.
Moving back to the topic of atheism and whether or not it is a religion; again, atheism says nothing about whether or not a person exhibits traits like dogged attachment and belief in a system of doctrines, but it at least rules out the supernatural aspect.
Most of what religious critics of atheist attempt to do is accuse all atheists of scientism. Scientism refers to the belief that nothing outside of science (such as aesthetics, poetry, profound experience, etc.) has any value. Few science-based atheists, not even the boogie man for religious people Richard Dawkins, fits that portrayal. Another aspect considered part of scientism is the idea that science should envelope every aspect of life and dictate all of our decisions (almost as if we were robots or Vulcans). Again, none of the usual suspects attacked by religious apologists, Sam Harris, Dawkins, Daniel Dennett, etc., fit this stereotype.
Of course, most of the aforementioned atheists are advocates of science and facts informing most of our decisions, and certainly all of our important decisions, but that is hardly an unreasonable position. Most devoutly religious scientists would agree with that. In science or any other topic of consequence, if someone makes a fact claim, it wouldn’t be acceptable to appeal to a gut-felling, a personal anecdote, or a holy book. Climate change policy decisions should be based on the best evidence found by professionals in or around the field of climatology; sex education policy should be based on the factual findings regarding the real-world consequences from each approach; pandemic responses should be based on the best scientific evidence available at any given point of time.
The most conservatively religious American Christians would agree that witch doctors and shaman shouldn’t be consulted about virology; astrology shouldn’t be consulted or taken seriously by astrophysicists; blood magic shouldn’t be attempted as a cure to pandemics; mysticism regarding chakras, crystals, and homeopathy shouldn’t be used in healthcare. Yet all the reasons why they would not take that sort of crock and woo-woo seriously is selectively reversed when the spotlight goes to their superstitions and mystical beliefs regarding Christianity. For them, praying to an invisible all-father (but only the Judeo-Christian one) can actually heal people; referring to iron-age superstitions is a good way to deal with modern social problems.
What scientific empirically-minded atheists do isn’t special. Atheist scientists simply use the same criticisms religious conservatives use against “pagan” and New Age mystical beliefs and subject all superstitious and mystical belief systems to it. Unlike the aforementioned Christians, atheists don’t exempt some superstitions from scrutiny and not others.
When the religious call atheism a religion what they’re really accusing atheists of is holding dogmatic unassailable views. While this could accurately describe some atheists, the vast majority of the time religious people are accusing perfectly reasonable atheists of this simply as an ad hominem attack against the atheist personally; it is a tool used in bad faith by the faithful to win an argument.
Similarly, many indisputably religious people combine this accusation against atheists with the maneuver of defining their own beliefs as non-religious. You will hear them say, “I’m not religious, I have a personal relationship with Christ.” Of course that statement is garbage because those people would indeed tick every box on the definition of the word religious; they believe the Bible is true and infallible (though they’ll define some of the more outrageous claims as “allegories”), they try to structure their lives by the system they (or an ecclesiastic authority) interpreted from the Bible, and they believe the supernatural claims in the Bible (again cherry-picking out the inconvenient stuff). They are indisputably religious, and this maneuver is absolutely intellectually dishonest.
All this is similar how Christians often mendaciously maneuver with the word faith. They trumpet off a list of things scientific atheists find more probable than “magic dunnit,” like the big bang, and say “it takes more faith to believe that than what they believe.” In reality, that isn’t the case. Atheists don’t believe “nothing came from nothing,” like Christians accuse. Atheists simply don’t claim to know what happened to cause the big bang or what existed, if anything, before the big bang. There’s no faith involved in their position. So none of this is proof atheists are exhibiting irrational faith or are religiously dogmatic.
To conclude, atheists cannot be religious, although they can be quasi-religious. But the atheists that get accused of it, such as Dawkins or Harris (or me), don’t even fit the definition of quasi-religious. It is just a dishonest tactic from apologists to protect the beliefs they’ve been indoctrinated into from scrutiny and legitimate criticisms.