Like many people, I have fallen into the trap of group think. Its a tempting safe place because it helps to shelter people from criticism and gives them a sense of belonging. I think that is the heart of the issue. People tare down others in order to prop themselves up. The internet has helped to bring non religious people together in a way that hasn't been done before, this can also be said of many other groups. So due to this growth, it was inevitable that the group would become split into different areas of though. A lot of friends I've had that use the term Atheist tend to gravitate towards specific you tube channels, writers, and bloggers. They build their views around these people and groups and then immerse themselves.
At one time my Identity was that of a Gay Atheist, So I was dedicated to defending anything Gay and Atheist, and occasionally resorted to rhetoric. I was blinded by my own fervor that I couldn't even hear outside opinions. I've grown up a little and learned that using labels and grops as shields helps to erase your own opinions and thoughts. So now I use labels as more of a starting point and work from there instead of trying to fit the label.
So I think the short end is that people want and identity and want to make sure that people are aware of it. Quite often people will adopt the identity of a group and will tare down those in the out group because of a false sense of superiority.
Its way more fun to just be by yourself sometimes and find your own thoughts.