I can't speak for all atheists, only myself. Its not that I'm trying to prove Christianity wrong, but, to get people to understand the Atheist side of the debate. To show, this is why we don't believe; History, Science, hundreds of other religions claiming to hold the truth as well, etc. To keep religion out of science classrooms, to promote good science, etc.
Greg Laden's Blog : Florida Academic Freedom Bill Passes in State Senate
I can't find the article now, but with this bill, kids can now say the Earth is around 6 to 10 thousand years old, in a Science classroom!
Some good videos:
YouTube - Atheist
YouTube - Why do atheists care about religion?
While I don't hold all of the same positions as this video, its pretty good.
Following videos are satire:
YouTube - The Atheist Delusion
YouTube - God Doesn't Exist? Prove It!
YouTube - Checkmate, Atheists!
I thought they were a little funny.
Edit:
I forgot to mention this, but atheists are considered the least trustworthy people in the United States. Don't you think thats a little wrong?