The "American Atheists" organization would disagree with you. The definition of atheism they put on their website does have a belief system and a specific philosophy. I counted the words "believe or beliefs" about 8 times in the definition of atheism they have on their site.
From American Atheists website:
The following definition of Atheism was given to the Supreme Court of the United States in the case of Murray v. Curlett, 374 U.S. 203, 83 S. Ct. 1560, 10 L.Ed.2d (MD, 1963), to remove reverential Bible reading and oral unison recitation of the Lord's Prayer in the public schools.
“Your petitioners are Atheists and they define their beliefs as follows. An Atheist loves his fellow man instead of god. An Atheist believes that heaven is something for which we should work now – here on earth for all men together to enjoy.
An Atheist believes that he can get no help through prayer but that he must find in himself the inner conviction, and strength to meet life, to grapple with it, to subdue it and enjoy it.
An Atheist believes that only in a knowledge of himself and a knowledge of his fellow man can he find the understanding that will help to a life of fulfillment.
He seeks to know himself and his fellow man rather than to know a god. An Atheist believes that a hospital should be built instead of a church. An Atheist believes that a deed must be done instead of a prayer said. An Atheist strives for involvement in life and not escape into death. He wants disease conquered, poverty vanquished, war eliminated. He wants man to understand and love man.
He wants an ethical way of life. He believes that we cannot rely on a god or channel action into prayer nor hope for an end of troubles in a hereafter.
He believes that we are our brother's keepers; and are keepers
of our own lives; that we are responsible persons and the job is here and the time is now.”
http://www.atheists.org/Atheism/
Atheists have the right to have all of these beliefs but people shouldn't deny atheists have beliefs (which happens a lot in these threads).