Tell her. Now. Or would you rather walk on egg shells for the rest of your life? The sooner you get this out into the open, the better. It isn't healthy to bottle feelings up, or to sweep important issues like this under the carpet - especially in a marriage. You only get one shot at life; one chance to be happy. If she doesn't care, well then great. If she wants to leave you, that's great too. You'll both be happier, whatever the outcome. Holding your tongue will make you both miserable.
Isn't it just easier for them to believe in heavenly rewards and the chance to see their long gone relatives again?
Not sure if you were being ironic, but I found that insulting. Why should we sit back, rational and "enlightened", while others waste their lives thinking it's only a test? I see it as a moral obligation to at least try to relieve those we care about of their superstitions. What you suggest is like figuring out the cure for cancer and keeping it to yourself. It isn't right.