Atheism is technically a religion based on the definition of a religion.
1. a set of beliefs concerning the cause, nature, and purpose of the universe, especially when considered as the creation of a superhuman agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs.
2. a specific fundamental set of beliefs and practices generally agreed upon by a number of persons or sects.
3. the body of persons adhering to a particular set of beliefs and practices: a world council of religions.
http://dictionary.reference.com/browse/religion