You're not making sense. You can't be an unorganized organized group. What are atheists talking about when they have these annual conventions? Did you look at the websites for their national organizations? The fact they have national organizations directly conflicts with your contention they are unorganized. The whole idea of organizing just to talk about something you don't believe in is absurd.
You like to make assumptions don't you? In real life, I don't preach to anyone and do not talk about my faith unless someone asks.
Then, there's the little matter that, in some spots like California, atheists actually have humanist centers where they go every Sunday, as a answer to their neighbors who attend church on Sunday. I saw this in an article from TIME magazine. According to one lady that was interviewed, she felt that it's tougher for atheists, when they have families, because unlike their Christian counterparts, they usually don't have support groups and centers to help raise their kids and pass their morals and values.
The term "atheist" and "anti-theist" tends to be interchangeable. The self-described atheists, on the sites you linked, don't just believe that there is no God. They are quite hostile to religion and religious people.