That is a mistake that religious apologists often make, because they think that they can prove that atheism is a belief, which is quite correct, it can be, ( Not always but sometimes.) but the mistake is in thinking that a belief is the same things as religion. But it is not.
A belief is something we hold as probably true without supporting evidence, where a religion is something we hold true without evidence but support with fake authority. As in. "Because my holy book says so." "Because my tradition says so. " " Because my God says so. " Etc.
Religion in short is the same thing as the fallacy of proof by authority. And is quite different from honest belief, which accepts that it is belief.
Atheism is not a religion, but good point that while many atheists disagree between themselves about many other things besides religious beliefs, they generally agree to disagree and often try to use reason and logic rather than violence to persuade others to their point of view, as evidenced on this site. We might see a "war of words" sometimes, but generally atheists find peaceful ways to deal with disagreements.
The war of words on this site has often been as violent as words alone can get. If this site is not an example of splinter grouping, I don't know what is. We cant' even agree on what the words agnostic, theist, and atheist mean, without name-calling and adolescent vulgarities. I have been verbally threatened with violence on this site more than I ever have anywhere in the real world.
@skado Well... Some of that comes from immature personalities who feel the need to be right about everything and the tone people take with each other.
Seems some of these personality conflicts are more about intention of asserting oneself than the substance of the points being made. My feeling about Agnosticism is that we are admitting that we don't know.
As I remember Joseph Campbell saying, something to the effect, "He who thinks he knows, doesn't know... He who knows he doesn't know, knows." That's a great attitude to have here on this site.