(recent Usenet post about Palin)
The argument--someone offered a version of it not long ago in a comment here--sounds right, but I don't think it is.
When you get on an airplane, do you worry about whether the pilot is a fundamentalist? What if God tells him to fly into a mountain? The mechanic who checked it? What if God told him not to bother—everything was fine? If you go in for an operation, is the question of whether the surgeon believes in evolution one of your main concerns? What if God tells him to cut out your heart and put it on an altar? When driving down the highway, do you worry that perhaps one car in ten coming the other direction is driven by a religious believer who might decide that this is his moment to go to heaven?
There is evidence all around us that people can hold apparently weird religious beliefs and still do a competent job of dealing with the real world. Perhaps that means that they don't really believe in the weird beliefs--that they are a story they enjoy telling themselves, not a real part of their picture of the world. Perhaps it merely means that knowing how to fly an airplane or use a scalpel doesn't depend on your view of religion, so pilots and surgeons who happen to have odd religious beliefs nonetheless learn and practice their professional skills the same way other pilots and surgeons do.
Whatever the explanation, I think it's clear by ordinary observation that holding weird religious, or for that matter political, beliefs rarely makes one unable to live one's life with an ordinary degree of competence.
And, of course, so far as Palin is concerned, the evidence most often cited—her supposed belief that the Iraq war is divinely inspired—is bogus, as I have already pointed out. Her actual remarks implied that she didn't know if it was God's plan or not, which suggests that she does not have voices in her head to answer such questions but must make up her own mind. Just like the rest of us.