If one is an atheist who desires to hold onto one's atheism rationally, one would appear to need some arguments that God does not exist. Many theists maintain that it would not do simply to refute arguments that God exists. That would--many theists maintain--only show that there was no good reason to believe that God exists. It would not show that there was good reason specifically to believe that God does not exist. Theists sometimes say: you canít prove that God does not exist, because you canít prove a negative; so atheism requires just as much faith as theism does; so at least you should be agnostic.
Atheists tend to counter with OccamsRazor?. If there truly is no reason at all to suppose something exists, then chances are it doesn't.
See also TheProblemOfEvil and FaithAndRationality.