As Prager explains it (linked up above) — the “something so secular” is actually a RELIGION. Yes, the seculars do have a religion, and that religion that is taking the secular world by storm comes under the “Church of Environmentalism”.
That “church” and that “religion” is what is on display in that movie.
They have the exact same religion as the Khmer Rouge.
And that road only leads to one destination.