I very much doubt the Inverse Fire is some kind of illusion or mind control device, since some Inchoroi must have invented it at some point, and they wouldn't want to use such a thing on themself. I imagine the Inchoroi culture, prior to the discovery of the Inverse Fire and damnation, was extremely nihilistic and hedonistic. I greatly doubt they believed in any Gods at all, or any morality that we would understand. Why would a member of a culture like that build a machine that forced the idea of damnation upon them?
I personally suspect they came across the invention of the inverse fire, the discovery of an afterlife, and the knowledge that there was objective morality and damnation, entirely by accident, in the course of other scientific inquiry. Naturally, the discovery and its irrefutability shocked and transformed their entire culture. Enough that they took their entire species to the stars to seek out the source of their damnation, and destroy it.