A Theist "knows" there is a God/Gods.
An Atheist "knows" there is no God/Gods.
IMHO, it requires every bit as much faith to believe there is no God as to believe there is...
That's why one shouldn't introduce the concept of "belief" or "faith" into the discussion. Establish your atheism as a scientific theory, and let your oppeonents prove your theory false.
The good athiest says, "There is no God". It's up to the person insisting a God exists to pony up his proof.
So far, no evidence to contradict the theory has been provided.