I would tend to agree that atheists don't normally have anything to bring them together, a lack of belief isn't something that binds people together. But then, just because a group of people were born Christian or Jewish, does that give them any more of a reason to band together? Perhaps just cuz they hold meetings once a week?
I think that atheists actually tend to be of a mindset that we aren't as socially needy. To be an atheist most often requires a bit of independent thought to begin with, and there seems to be a genetic predisposition to a belief in a deity, so perhaps those things go together. Group-think & atheism do not mesh.
But, given a common enemy, atheists are joining together, and raising their voices louder, and hopefully we can continue to speak for everyone's rights to be free from religious oppression.