Several things.
One thing I noticed coming from a 'fundamentalist background' , many people who come from the very conservative upbringing tend to be indoctrinated in the 'black/white' , yes/no, binary thinking. Something is either true or it is false, no shades of grey between. In the case
of many 'ex-fundamentalist' who have become atheists, that seems to be a factor (not that it is wrong, it is just that the shades of grey are overlooked).
There are a lot of shades of grey out there. As a matter of fact, much of the religious method of learning/teaching in Judaism is arguing about the shades of gray (and all the colors of the rainbow and then some) about the meanings of various scripture.
Of course, just because there are shades of gray, it doesn't mean either white or black is the WRONG choice.. it is just so many choices are being overlooked for consideration.