[Jacob_Gilliam]

The error in your post is that belief entails that you believe in the existence of something, not the lack thereof.
In order for atheism to be a belief, it would have to refute something that can demonstratably be shown to be true. True, if God exists then atheism is wrong, but that does not make atheism a belief because atheism does not refute anything known nor does it suggest the existence of anything which cannot be or is not proven. The unicorn principle does hold up because over the expanse of human existence many religions have "died", and today there stories would be considered mythology, but in the past would have been considered true (by those who practiced those beliefs, such as Greek mythology).