As a wedding cake baker I have pondered this very situation. My decision, should I ever face it, will be to jack my price up way high, (I have no fixed prices so I can get away with it) and tell them that any one I bake a cake for I spend a lot of time praying for, that they will meet the maker of the universe and get their lives in order.
See my post 15 for another way to get past it.