Do you have a mind? Even though none of us has ever seen a mind, we all believe in our minds. Same principle applies to faith.
Atheism requires much more faith than Christianity or belief in God. Atheism believes in just matter. Interesting issue is that when an atheist loses a loved one to a horrible crime, they will want justice.
By desiring justice, the atheist has internalized their grief and loss and now is touching on the spiritual component inside themselves that was put there by guess who? GOD.