"Our life is shaped by our mind; we become what we think. Joy follows a pure thought like a shadow that never leaves."
― Buddha
Buddhists are atheists, buddy.
Buddhism is a nontheistic religion. In the Gallup data in the OP they fall under the catagory of non-Christian religion.
Given the target audience who better to challenge to words of one agnostic then those of a wiser agnostic.
http://www.religionfacts.com/theism/buddhismOne doctrine agreed upon by all branches of modern Buddhism is that "this world is not created and ruled by a God." {1} The Buddha himself rejected metaphysical speculation as a matter of principle, and his teachings focused entirely on the practical ways to end suffering.
On the other hand, the Buddha did not explicitly rule out the existence of a God or gods.
Buddhism is atheistic, but spiritualistic. My Mills quote was about the nonimportance of happiness as a criterion, that religious people are more happy does not immply that this is good, or that people should belive, its just another selfish thing to do against the good of your species. I also have a problem with atheists, because, like Buddha they remain spiritualistic, or rather while they explicitly claim they are atheistic they still share the values of the religions common in their society instead of forming a positive doctrine and re-evaluate their own values. The clash between religion and atheism is a false one, the real issue is the clash between reason and tradition. Only in this aspect, I think the spread of atheism is good, as the end of tradition that produces the possibility of new things to come.