Because like every other ideology prior to it – humans are involved. Humans like to label things this or that way, define something this and that way, narrow the scope of something this or that way…it’s just another trend in the ideological cycle.
I like atheism, I also hate atheism. In the same vein, I like Christianity, I also hate Christianity.
Nothing is really living at it’s ‘ideal’ – everything has been corrupted by the human need to control it. I have met lots of great atheists in my time, I have also met my fair share of people that ruin it for everyone else.
Atheism is going to enjoy some of it’s ‘heyday’ right now and maybe for the next 15 to 20 years. But like everything else it will also fall – mistakes will be made to taint what seems like such a bright endeavour. So that when it’s finger that wags at people unlike it will reveal there are 4 others pointing at its-self. Such is life.
Atheists believe there is no God, it doesn’t mean they don’t believe in something else.