Is atheism a religion?
Is atheism a religion? is a question atheists are often asked, although it's sometimes not asked, but rather stated, "atheism is a religion." I understand the confusion because there are several points of commonality between the two: many atheists "religiously" hold gatherings where they have "communion" with each other and discuss belief in gods, souls, and the supernatural and "evangelize" their position and try to "convert" people over to it. To many people, this behavior is very similar to the behavior of religious people, so they conclude that atheism is a religion. However, while there are surface similarities, atheism is dramatically different from a religion.
Religions are opt-in
Excluding the most violent adherents, most religious people accept that a person is only part of a religion if they choose to be part of it. Thus, a Hindu is a Hindu because they have decided to adhere to the tenants of Hinduism, and everyone who doesn't follow the Hindu religion is not a Hindu by default. Atheism is like the default position when a person doesn't follow any religions. A more pithy way to say this is, "atheism is a religion like not collecting stamps is a hobby."
Generalizing "religion" too much makes the word meaningless
If the word "religion" just means people gathering together to discuss any shared interest, then suddenly everything becomes a religion from fantasy football leagues to scrap-booking groups. Of course, very few people would understand these activities to be religions, and certainly wouldn't think of them when the word "religion" is used.
Religions believe in the supernatural and hold rituals
While all religions are different, they do share two common traits: the belief in some form of supernatural phenomena (gods, spirits, afterlife, etc.) and an adherence to ritual (prayers, rites, tenants, etc.). Atheism is merely the lack of a belief in gods; there are no supernatural beliefs or rituals of any kind.
Some religious people are atheists
To add to the confusion, some religions, like certain forms of Buddhism, do not believe in gods. Therefore, those Buddhists are technically atheists even though they believe in souls, pray, and religiously perform rituals. Of course, religious people rarely identify as an atheist, because they equate atheism with being non-religious even though it technically isn't.
You can debate a belief without believing in it
This should go without saying, but a common argument in favor of atheism being a religion is that atheists often talk about belief in gods. Of course, just how political pundits can criticize liberal politics without being a Liberal, so too can an atheist criticize theism without being a theist.
- youtube.com/watch?v=OmDaUO61jhA - Genetically Modified Skeptic - Is atheism a cult?