Many people (all of them religious, by the way) have asserted that atheism is a religion of some sort. It is not. Religious belief is based on faith. Atheists do not have faith in a higher being. That lack of faith has been portrayed by some as just another form of faith. The claim is that religious people believe in a god or gods, while atheists believe there is no god. This claim makes the two parties to this controversy appear to be basically the same, with equally valid but divergent viewpoints.
Religious people believe in the supernatural, while nonbelievers do not.
That claim is simply not valid. Faith and a lack of faith are not two sides of the same coin. Believers and nonbelievers are starting from different places and they view everything with different perspectives. Supernatural refers to something other than the world around us; it is a concept that there is something “out there” to which the laws of physics do not apply. There is no credible evidence for that assertion. No properly designed and conducted experiment has ever provided any verifiable evidence of gods, demons, devils, ghosts, zombies, poltergeist, or any of the other nonsense with which people like to fill their heads.
The comparison between religion and atheism is exactly like the comparison between astronomy and astrology. The idea that they are somehow equivalent is just false.
Many have alleged that the complexity of the world we live in is proof that it was created.
They claim it could not have just “happened”. Well, it could and it did. Statistically unlikely things happen all the time. For example, to the best of our understanding life on Earth began when some amino acids grouped together and at some point formed a compound that was capable of producing copies of itself. It was certainly an unlikely event. But the stuff to make living things were lying around for a billion years or so and during that long a time some very odd things will occur on occasion. All it takes is for the proper conditions to come together once or twice. Once life begins, the process is self-sustaining.
Some physicists have calculated that if a few very basic items, such as the fundamental unit of charge, were slightly different, this universe would have unfolded in a very different manner. If any of those basic constants were different by a few percent, stars and galaxies and planets and humans would never have been formed. It has been argued that this is evidence that our universe was created. Well, we do not have a clear idea of why these fundamental parameters are what they are, but we do know that if they were slightly different we would not be here to measure them. Basically, this argument just states that because we are here there must be a god that put us here. There is nothing logical about that reasoning. The conclusion does not follow from the premise.
Is atheism a religion?
Is atheism a religion, with different tenets perhaps, but basically part of the same process that leads people to other religions? No, it is not. Atheism is a lack of religious belief rather than another form of it.