Holy Mother Church disagrees with you then. It is the Year of Faith commemorating the 50th anniversary of Vatican II so I am trying on CAF to draw attention to the wealth of knowledge contained in the documents of the last ecumenical council. The Second Vatican Council, in analyzing contemporary atheism, indicated that the word “atheism” covers quite different realities:
“…The word atheism is applied to phenomena which are quite distinct from one another. For while God is expressly denied by some, others believe that man can assert absolutely nothing about Him. Still others use such a method to scrutinize the question of God as to make it seem devoid of meaning. Many, unduly transgressing the limits of the positive sciences, contend that everything can be explained by this kind of scientific reasoning alone, or by contrast, they altogether disallow that there is any absolute truth. Some laud man so extravagantly that their faith in God lapses into a kind of anemia, though they seem more inclined to affirm man than to deny God. Again some form for themselves such a fallacious idea of God that when they repudiate this figment they are by no means rejecting the God of the Gospel. Some never get to the point of raising questions about God, since they seem to experience no religious stirrings nor do they see why they should trouble themselves about religion. Moreover, atheism results not rarely from a violent protest against the evil in this world, or from the absolute character with which certain human values are unduly invested, and which thereby already accords them the stature of God. Modern civilization itself often complicates the approach to God not for any essential reason but because it is so heavily engrossed in earthly affairs…believers themselves frequently bear some responsibility for this situation. For, taken as a whole, atheism is not a spontaneous development but stems from a variety of causes, including a critical reaction against religious beliefs, and in some places against the Christian religion in particular. Hence believers can have more than a little to do with the birth of atheism. To the extent that they neglect their own training in the faith, or teach erroneous doctrine, or are deficient in their religious, moral or social life, they must be said to conceal rather than reveal the authentic face of God and religion…In her loyal devotion to God and men, the Church has already repudiated(16) and cannot cease repudiating, sorrowfully but as firmly as possible, those poisonous doctrines [of atheism]…Still, she strives to detect in the atheistic mind the hidden causes for the denial of God; conscious of how weighty are the questions which atheism raises, and motivated by love for all men, she believes these questions ought to be examined seriously and more profoundly…She courteously invites atheists to examine the Gospel of Christ with an open mind…”
***- Gaudium et Spes (PASTORAL CONSTITUTION ON THE CHURCH IN THE MODERN WORLD), 1965 ***
While objectively atheism as an ideology is sinful, in that it rejects God, subjectively on the personal level there are a great many issues which the church recognises can make a person turn to atheism without thereby incurring sin ie their conscience is in error. In other words its an error but not wholly unintelligible.
Even Catholic mystics underwent periods of de facto atheism when they doubted the existence of God, during a dark night of the soul. Consider Saint Therese of Lisieux:
**St. Therese of Lisieux, Doctor of the Church, describes herself as having extreme doubts of God’s existence. She called the atheists of the time her brothers and sisters and imagined herself dining with them. **
“Having known the painful ordeal of religious doubt and even the night of faith, Thérèse united herself in mysterious solidarity with non-believers. Convinced that all human beings have the right to know themselves loved by God, she wanted to reach them all”. - Cardinal Angelo Sodano, Secretary of State (1991).
Thérèse of Lisieux directly confronted anguish in the face of death. The atheist’s questions about the existence of God and of an afterlife became her problem when, in her trial of faith, she was suddenly submerged in an abyss of anguish and there experienced the distress of nothingness. She was deprived of what she calls “the joy of faith”; she could not "enjoy this beautiful heaven on earth."21 She entered a place of deep darkness that surrounded her and threatened to overwhelm her. She seemed to hear the darkness say: "You believe that one day you will walk out of this fog which surrounds you! Advance, advance; rejoice in death which will give you not what you hope for but a night still more profound, the night of nothingness."22