While believing strongly, without evidence, is considered a mark of madness or stupidity in any other area of our lives, faith in God still holds immense prestige in our society. Religion is the one area of discourse where it is considered noble to pretend to be certain about things no human being could possibly be certain about. It is telling that this aura of nobility extends only to those faiths that still have many subscribers. Anyone caught worshipping Poseidon, even at sea, will be thought insane.
Sam Harris, Letter to a Christian Nation
ADDED: If you really believe in the power of prayer to cure illness, why am I certain you'd never pray that your poor diabetic grandma will grow her foot back? You believe God will cure cancer or disease through prayer, so why does God hate amputees so much?