The earliest Christians were accused of all sorts of things that may seem preposterous to us now, like bacchanalia, cannibalism, and even atheism. But Karl Barth noticed that amongst the absurdities leveled against them, the charge of atheism was most definitely true – and should be of Christians in all ages. He writes in the Church Dogmatics 2/1:
It was no mere fabrication when the Early Church was accused by the world around it of atheism, and it would have been wiser for its apologists not to have defended themselves so keenly against this charge. There is a real basis for the feeling, current to this day, that every genuine proclamation of the Christian faith is a force disturbing to, even destructive of, the advance of religion, its life and richness and peace. It is bound to be so. Olympus and Valhalla decrease in population when the message of the God who is the one and only God is really known and believed. The figures of every religious culture are necessarily secularised and recede. They can keep themselves alive only as ideas, symbols, and ghosts, and finally as comic figures. And in the end even in this form they sink into oblivion. No sentence is more dangerous or revolutionary than that God is One and there is no other like Him . . . Let this sentence be uttered in such a way that it is heard and grasped, and at once 450 prophets of Baal are always in fear of their lives. There is no more room now for what the recent past called toleration. Beside God there are only His creatures or false gods, and beside faith in Him there are religions only as religions of superstition, error and finally irreligion.
So be an atheist. If you aren’t, you may not believe in anything at all.