Post Christian societies are much more resistant to repentance as it is much worse to see the Truth, and then deny it, than to never have heard the truth at all. Blasphemy of the Holy Spirit comes to mind.
Romans 1:18-32 is more specific.
Revelation tells where these “post-Christians” will go and what they will do.
Frankly, I’m betting that some now Muslim leader claiming the caliphate will announce a new poofter friendly / mandatory form of Islam and will be able to pull in the West’s “progressives” in droves.