de budding,
"How do you qualify atheism as different from religion/belief systems?"
It is simply non-committment to the beliefs of others, it is not an activity. If someone claims to be a Christian does that mean Christianity is a systems of disbelief of every other belief system in the world. Christians are only slightly less atheistic than myself, Christians reject the entirety of all possiable gods accept one, I reject them all, the difference, one god. May Zeus be with you!!