Perhaps the idea is that certain Christians have a direct inner spiritual experience of God/Christ that most ordinary people including some other Christians lack. Everyone would have this experience but Satan has blocked this in a bid to allow people to have freedom of will to reject God and join him as a follower in hell. So all she would be doing in this film is not forcing people to become Christians but removing the spiritual block Satan has put in place.
He completely misses the point of why people on the whole would prefer to have a faith than to lack one or just simply believe in science and nothing else. His logic may well be solid and well reasoned but his lack of empathy and understanding of his fellow man is so staggeringly immense it would darken the stars if manifested into physical form.
None of this has any bearing at all on whether God or supernatural beings actually exists or not however. You can have all this instinct driven psychology and a real God who actually exists as one thing doesn't exclude the other.
Well there was the reign of the five good emperors Nerva, Trajan, Hadrian, Antoninus Pius and Marcus Aurelius none of them were Christians. They did persecute Christians to some extent but aside from that.
An interesting fact is that Muslims back in the day didn't really want to everyone they conquered to convert to Islam. If they converted to Islam they would end up paying less tax. The conquered peoples were paying the same tax to the Byzantine and Persian empires so they didn't really mind their new overlords.
If atheism is true (i.e there is no supernatural element to the universe only properties of matter/energy) then objectively we are all robots based on DNA programmed by environmental stimulus. If that's how it is then that's how it would be if it's true you wouldn't get to argue with the facts if you don't like the idea. If your dad said "Hey I fucked your mom dude!" you may not like him saying this but it happened nonetheless you don't get to argue with him about it.