About 200 years ago a man named nietzche predicted the decline of Christianity ..which he considered to be inevitable and impossible to reverse even if we would want to.
He also predicted that the resulting nihilism would make the 20th century the bloodiest century in human history. Which it was.
he predicted that there were 2 possibke outcomes for the loss of a serious religion (because sure...plenty of people still claim to have a religion but the vast majority of those people are not serious): the Uberman, who is able to find purpose in the thriving and advancement of his people (nazis for example)...and the last man who simply becomes apathetic and shallow about everything...the possibility of which horrified nietzsche the most.