Geemack,
I've never understood why it is okay to tell others why it is not okay for them to express opinions, then in the same breath, express your own. We all have an agenda or two, so what?
The "rules" of geocaching are not very complicated and the only real rule is to use common sense. There are a few no-no's like tabacco, ammo, fire arms, liquor, etc., but that's about it, and those are "common" sense.
I don't think any of us want to start defining what is okay and not okay in a cache. Stick with the common sense idea.
Okay, you may not be religious, that's your choice. Let's stick with the original question, is it okay to put religious materials in a cache? Answer: Sure. (You may not like it, but others may.)
Is it a great idea? Not in my opinion, but neither is a I wouldn't call anyone names or pin labels on them. I don't like everything I find in caches, but that's okay, others will.
Geocaching is about the hunt not the treasure.
Enjoy the hunt!
luv2fish