Roughly 1/10 of Americans, or 10%, don't believe in a god. Well, specifically, 1/10 adult Americans. But according to a Gallup survey only about 2% call themselves atheists, and maybe another 2% agnostic. Why do the majority of people under a more broad definition of atheism (simply lacking a belief in a god) not call themselves atheists? After all, most Christians call themselves, well, Christians.
Well the answer is because the word atheist has been so demonized. Literally. Atheists are often believed by the devoutly religious to worship and believe in a literal devil. I myself met someone who had that belief. So this massive ignorance on the basic beliefs or non-beliefs of atheists is promoted by alas, people on the Christian right-wing. This tidal wave of ignorance washes over the rest of America, including those who happen not to have a belief in a god.
So while those who don't call themselves atheists, but lack a belief in a god, do not necessary believe atheists worship a devil, they buy into the negative image of atheists that those on the Christian right-wing (or even Christian mainstream) promote. 300 years ago atheism literally was another word for evil. Those who were atheists were considered evil. Thankfully it is not quite defined in this way anymore but it is time atheists get our word back and stop letting those who despise and fear us, control it. Groups such as American Atheists promote atheism and defend it. We can use your help.