The Axial Age shows the confusion that arises over ‘religion’ and the danger of generalizing on the subject. We see a whole spectrum of emergent clusters: from China to Rome: buddhism, monotheism, but also the real birth of ‘secularism’ in Archaic to Classical Greece.
In modern times it looks like civilization is moving beyond religion, but the modern begins with the Reformation, so ‘religion’ is reinjected into modernity from the start. That said, ‘religion’ begins to remorph rapidly, and by the time of figures like Kant/Hegel/Schopenhauer the whole subject is no longer ‘religion’ in the classic sense. And then we see the system swing to an extreme opposite in the revolutionary left’s adoption of reductionist materialism. The latter confused the issue, however, and drove many to resist the modern pitch.
The mistake was to focus narrowly on the barren materialism of the positivist age.
It is important to be wary of the recent trend toward making ‘secularism’ synonymous with atheism, reductionism, scientism, and darwinism. Secularism as noted began with the Reformation. But the larger field of secularism comprises a complex constellation of opposites: religion, science, mathematics (in a huge explosion in the wake of calculus) liberalism to socialism/communism, economism (capitalist and thence general postcapitalist economic systems) ideas of freedom counterpoint to determinism, the tenor of the Enlightenment (in its many varieties, French, German, Scottish, etc…), global religion with early modern takes on Confucianism, Taoism, Hinduism, Buddhism, etc…Schopenhauer almost reinvented buddhism with his version of transcendental idealism..
In a word the ‘secular’ is a vast field. We should not let fanatics cripple it with narrow definitions.