But there ARE atheist churches--and I don't mean UU churches, or Scientology churches, or Buddhist temples. There are 'Sunday Assemblies' for atheists (a concept which was started by a couple of British comedians), there's the Church of the Flying Spaghetti Monster, there's the followers of the Invisible Pink Unicorn, etc. But you'd be hard-pressed to find anyone attending one of those meetings claiming it's their 'religion', whereas Scientologists, for instance, WOULD claim that they practice a 'religion'.

'Atheist' is just a person's answer to exactly one question ('Do you believe there is at least one god?'), and doesn't tell you anything else about a person's beliefs. It doesn't tell you if they're a skeptic, or their politics, or their favorite sport, or what their ethical code is--same thing for 'theist'. That's how you can have atheists who also believe in ghosts, alien Elvis, or fairies at the bottom of the garden. Or theists who are One Percenter bikers, for that matter.

...And that doesn't even begin to touch on the quagmire that attempting to define 'religion' gets you into.