The majority of GAF represent a minority of America that actively lashes out against and condemns Christianity. They take examples in the news of extremist "Christians" who misbehave, apply that behavior to all followers of the religion, and disregard any claim to the contrary.
I call strawman.
Most of us "unbelievers" simply feel that religion should not become public law, and that religion has no place being taught in the classroom as fact, and that folks of differing beliefs should never be held to the laws and creeds of one particular religion.
We don't hate you; we just don't CARE that you think abortion is bad and should be legislated against in all cases; we don't CARE that you think homos are evil and should never have the opportunity to enter into formal marriage; we don't CARE that you think the world was created by an omniscient being and that all laws made on Earth should acknowledge that belief; we don't CARE that your rigid sense of morality is offended by naked boobies during the Super Bowl.
We're for a minimum set of restrictions on human behavior in those cases when the harm to another is not clearly delineated, preferring to give the benefit of the doubt to the accused. Rather than endorse one religion in codified, federally sanctioned form, we prefer to endorse NO religion, and instead let religions endorse themselves on their own time and dollar. We prefer the observable, empirical, and scientific because they are the most common of all to our shared perspective.
It's a society of TOLERANCE, and we accept those of you with religious beliefs as a big part of it, but we don't intend to let you expand the rules at the expense of even a minority. Your faith should be strong enough to survive such a notion, and your common sense should be strong enough to realize that this is the best compromise for a democratic society as a whole.