Most atheists (myself included) lack belief in any kind of higher power in general because of lack of evidence for such. We do not actively assert there is not one because how could we know? Most of us DO actively assert the non-existence of specific God claims because said claims are usually specific enough that they can be demonstrated to be false.
Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.
Albert Einstein
Albert Einstein