Any belief for or against God, is a religion?
On its own, conversationally? no. When it is practiced with all the trappings of a modern religion bar the diety, yes. Sunday school, synods (they use the term to define some of their gatherings), their doctrines ... they have established that type of theism at a level of organization that rivals plenty of other recognized religions. Perhaps I cannot properly define it, but I know it when I see it. Here is another take at it ... is monotheism a religion? Unarguably yes. So what about polytheism? You would have to say yes (amen?). So why wouldn't atheism (nihilism?) follow as well? Atheism, as currently practiced (another defining characteristic, no?) is a de facto religion.