They can be, so can churches and preachers. That doesn't make them bad people. An atheist is simply someone with the lack of a belief in a deity, they do not claim to know god does not exist. I am an agnostic atheist, in my opinion a god could exist because we cannot know either way. But since the burden of proof is on the theistic claims, it is illogical to believe in them until that burden is met. as of now, it has not been met.