If you are not a Muslim you probably don’t identify yourself as a non-Muslim, and you would agree with me when I give you the label non-Muslim. We don’t walk around identifying ourselves by a negation of specific beliefs. That would be a waste of time. You don’t get on Facebook and type in non-Muslim, non-Hindu, non-Jewish, and non-Buddhist in your religious views. You would agree these views are not religious belief, the religion you identify yourself under is your religious belief. So what about the term atheism?
Atheism is a negation of all religious belief and it is a useful term, unlike the term non-Muslim, which is only useful in context. Atheism is a lack of belief and applies to all who don’t believe in deities, just like the term non-Muslim applies to every single person who’s not a Muslim. Our language has become distorted in this area and needs clarification. By this simple reasoning, we can label all people who don’t believe in deities as atheists even if they refuse to acknowledge this because of the negative connotations associated with the word atheist.
If you are a Christian, you are inherently a non-Muslim, non-Jew, non-Hindu, non-Buddhist, non-pagan, etc. But if you are all these plus a non-Christian who doesn’t worship any deity, then you are an atheist. That’s what the word means.