Before he became Pope John Paul II, Karol Cardinal Wojtyla (in a letter to French theologian Henri de Lubac) analyzed the state of the world this way:
The evil of our times consists in the first place in a kind of degradation, indeed in a pulverization, of the fundamental uniqueness of each human person.
He had in mind especially the "atheistic ideologies" of Naziism, Communism and scientific materialism that reduce persons to objects of use. And he proposed that the Church respond by offering,
a kind of “recapitulation” of the inviolable mystery of the person.
He dedicated his subsequent pontificate to the task. He did it perhaps most fundamentally and prophetically in and through his theology of the body. That profound exploration of "the inviolable mystery of the person" teaches us that we are "made in the image and likeness of God" not only as unique individuals, but even more completely in communion with one another. The self-donating, other-receiving, life-giving union of a man and a woman in marriage is an icon not only of the relation between Christ and the Church, but relations within the Godhead, the Holy Trinity.
A theological discernment enables us to see in our time two unexpected threats (almost like two “apocalyptic beasts”) located on opposite poles: on the one hand, the idolatry of Western freedom; on the other, Islamic fundamentalism: atheistic secularism versus religious fanaticism. To use a slogan, we find ourselves between “gender ideology and ISIS”. ...From these two radicalizations arise the two major threats to the family: its subjectivist disintegration in the secularized West through quick and easy divorce, abortion, homosexual unions, euthanasia etc. (cf. Gender theory, the ‘Femen’, the LGBT lobby, IPPF …). On the other hand, the pseudo-family of ideologized Islam which legitimizes polygamy, female subservience, sexual slavery, child marriage etc. (cf. Al Qaeda, Isis, Boko Haram ...)
These two "apocalyptic beasts" have the same root: a denial of the inviolable mystery of interpersonal communion.
It's interesting to note that the point in common isn't atheism, but lying views and uses (master/slave views and uses) of human sexuality. (How I love him for that focus on the evil of "female subservience"!)
It's not that the devil doesn't believe in God; it's that he hates Him, and he hates His image in us and in marriage.