KNOWLEDGE (Agnostic = I don't know. Gnostic = I know.)
BELIEF (Atheist = I lack a belief. Theist = I hold a belief.)
These are not mutually exclusive. For example I'm an Agnostic Atheist for the general god question. If you asked me if I believed in the Christian god as demonstrated in the Bible I would say I'm a Gnostic Atheist, because the properties of said god are contradictory, and many of the claims of the bible have been disproved. Some people find labels useful. I don't as it just muddies everything, because so many people (and every dictionary it seems) have different definitions.
Those atheists clean up highways for the same reason that religious people get together. Not necessarily to discuss the universe or criticize others, but to have a sense of community. I'm an atheist who grew up as an only child and I feel like I've always been fine alone, but not everyone is. It's also a good way to combat the dirty word that atheist has become.
Also just remember that there are thousands of religions with thousands of different opinions on an afterlife or whatever. If you have an idea about god then you automatically have dismissed 99.9999% of all the other religious ideas. There are some religious ideas that you will not entertain for a second. You got into this a little bit with the moon made of cheese. What if someone said God was a polar bear who was floating on the ice berg that is the universe? What reason would you have to dismiss that over "God is energy", "God is love", or "God is the son of a virgin." What about the people who claim right now that God is talking to them? Not just the crazies yelling on the street corner but people in government positions in the United States. The consistent position would be to dismiss them all until evidence was brought forth. Remember these aren't simple claims. This isn't you trusting your friend when he says he saw Brad Pitt yesterday. These are extraordinary claims which as the saying goes require extraordinary evidence. It's also worth asking what makes you think that this god would be loving? That the god would be worthy of worship? I don't know about you, but the idea that a God would offer a reward and punishment for abiding by his rules is quite a demented one.
Pat Tillman was an atheist in a fox hole. There are groups of armed men and women who are atheists who everyday try to combat this myth.
Sorry to go on (how do I make spaces!!) it's just that this subject fascinates me. Maybe you guys should do a topic on Skepticism of which atheism is a subset. Skepticism incorporates critical thinking and scientific inquiry to examine subjects like ghosts, conspiracy theories, psychics, claims of religion etc.
PS: Very nice snoring sound effects.