Atheists are almost all democrats, as few as they are, minuscule in numbers actually, but they do fight America and conservatism with passion and they have influence at the top of the left and media.
I don't know how you got losing 20% of the GOP from reading that post.
I got it from this in the article:
“‘Conservative’ isn’t a synonym for ‘religious’,” said American Atheists president David Silverman in a statement announcing the booth. “In fact, a fifth of conservatives seldom or never pray, and the same number state religion is not important in their lives.”
Granted, that is a quote from an atheist, so you have to take it with a large grain of thought. So maybe it is half that, say 10%. Whatever the number, unless it is completely negligible, I don’t see have we win by subtraction. But I am not an ideological purist, so your mileage may vary..