Man I wish you would have worded that a tiny bit different. Atheism is not a religion, thus a group of atheists does not make a "religious group" It makes a group of individuals, who only have an agreement in one subject, religion. They all know is a bunch of crap, that's about it, in all else they just may disagree on.
Religion is any belief system of ultimate values that shapes our pursuit of a particular kind of life in this world. This is the reason that it is quite fair to call atheism a religion, and Christianity as well.