There are reasons why some people would rather call themselves skeptics or freethinkers instead of atheists, and one is to avoid the not uncommon misconception that atheism automatically means the positive claim that there is no god.
One of the most common reactions I hear from theists on atheism or even on freethought in general is a question on where the nonbelievers base their morality considering they do not hold themselves accountable to an absolute standard or have their actions confined by the threat of eternal fire.