Back to the religious discussion, I'd say overall that it's pretty safe to say that most wastelanders are atheists. It would be hard for most people to have faith in such a dismal situation.
I agree that a lot of wastelanders are Atheist. It makes you wonder how these post-war religions/pre-war religions are managing to spread as much as they are? I guess the Church of Atom kinda makes sense in how popular it is, only because they believe the nukes were actually a good thing and make it sound like, to an outsider who has no idea about the past or about other religions, that the bombs were actually a miracle. Kinda like how people in Caesar's Legion believe the bombs fell because Mars dropped them from the sky so Caesar could take over. It honestly surprises me other religions that don't involve bomb worship are still out there. Honestly in post-apocalyptia, if a Mormon missionary came up to me and said there's a loving God that has a plan for all of us, I'd look at him like he's nuts and proceed to point to the Deathclaws and giant nuclear craters all around.
I doubt a lot of wastelanders even have a concept of life in the pre-war eras. They really only know the here and now. I would think that would basically halt a lot of old world religions and post-war religions right there outside of the basic concepts. Imagine you're a Wastelander who has no knowledge of pre-war life, you only know what you've seen, and someone starts talking to you about places like Babylon, Eurasia, Jericho, Jerusalem, etc, these people would have no point of reference for any of this and think it's simply a fairy tale.
On the other hand, depending on how they interpret it, they may think all those places missionaries are talking about took place here in America. Such as the Sorrows in Honest Hearts. When they were told about Jesus's birth they thought Daniel was referring to The Father of the Cave's deceased wife and child, just with the tacked on fact that the child died for everyone's sins. It's certainly interesting.
Heh, actually, I bet if you walked around with a cross necklace in the Mojave, people might think you're a Legion supporter because they would most likely equate the cross with Caesar's crucifixion tactics, not the Bible.