We have a basic mainstream culture that is as wide as we define our society. Within that mainstream culture, there are various subcultures and countercultures.
In the sixties, there were by necessity the emergence of these countercultures into the mainstream to fight for freedom and equality. But right now these countercultures have become destructive and counterproductive. that don't enhance the main culture but serve to further divide the society at large. It isn't isolated by just the present day but has happened any number of times throughout history.
As countercultures become more defined and delineated the main society becomes more fractured.
Take music. We use to have in the not so distant past a myriad of different types of music that we as society enjoyed, but now each genre is well defined and the mainstream society is fractured it what it enjoys. The industry as a whole is less inclusive and acceptive of its audience types.
Now how does this relate to atheism. Well, I'll tell you. It is the confusion of who and what we are. We are perceived as a counterculture instead of individuals.
Most believers think that atheism is a subculture all its own. They view it as like a religion because they can't understand an individual decision. The truth is that an atheist is not a person belonging to an organized belief and that atheists each are as fractured into subcultures as any other person. A southern atheist could be as conservative politically as any other southerner. What believers can't understand is that an atheist cannot be defined by his/her lack of belief in a deity.
An atheist is just as apt to be a mass murderer as an upstanding citizen. Atheism doesn't predict or determine the person or the counter/subculture that they belong to. It only describes one subculture that they don't belong to. This is why atheism can never be a movement. There is no coherent ideology or subculture that binds all atheist into a cause.