Wrong colors, wrong impression. You really don't want any religious symbols, if you are promoting atheism.
Talk more about why atheism.
There has been far too much talk about why not religion. The points against religion has been over emphasized. Not that they are invalid.
Religion itself, does that type of repetitive brainwashing. So the approach needs to be far more positive about atheism itself.
Atheism is perceived as negative, because of that over emphasis against religion.
Think positive, as well as make a "positive" cover approach. That actually is as well a atheistic approach.
In marketing, the positive approach works better, than the negative divisive approach. Your cover needs to be that positive.
I'll give you a bad example that shouldn't be taken. Your second cover is far too much like "Buckland's Complete book of witchcraft" cover. That book already has a negative connotation.