Only religious people say atheism is a religion, it's not. It's simply a non-belief in supreme entities. That is the single thing all atheists share.
Actually, it is quite a bit more then that. It is a challenge to the a prior claim of a competing belief system.
Atheism is always accompanied by an often unstated supplementary set of assumptions or faith. The characterization of it as a religion is defensible on logical grounds.
Where the arguments against religious faith usually go astray is that they attempt to introduce an arbitrary and illogical division between faith in religion and faith in other things. They then attempt to argue against religion while totally ignoring "other faith".
Humans don't live in a vacuum. We cannot like a computer shut ourselves off and stop. We are all ongoing and actively developing entities. Rejecting a faith is never a simple matter of removing a set of beliefs. It is ALWAYS a replacement of one religion with another or if you prefer a replacement of one set of core beliefs with another. These new beliefs whatever they may be are also ultimately just another faith.
Take the hardcore nihilist. If you push him to define and defend his beliefs you will usually after some digging drill down into something like Nihilism = True or "The entirety of the universe including the creation of the universe is random." They can't prove this they simply take it on faith. It is the core foundation of nihilism. The rock or soggy sand of nihilism if you will.
As I personally lack the wisdom to disprove nihilism the best I can do is point to the dangers in the faith direction of nihilism and hold up an alternative. Nihilism ultimately is based in a priori faith.
The nihilist are honest in their arguments and I respect them. They reject faith in God while simultaneously outlining and defining the faith they are basing their attacks from and advocating as a replacement. Most of the Atheist are far less honest. These illogical or dishonest arguments try to limit the conversation to simple attacks on religion without any attempt to define the belief structure they are using as an alternative. These attacks usually go something like "I just don't believe in your flying spaghetti monster and don't want to talk about what I do believe in." These types of arguments are childish and logically unsound noise.
Questioning one's faith is ultimately a good thing. We need to be introspective and examine what we really believe in and why. If we don't we will never know if we have structured our faith on something solid or something unsound.