1) Most Xns believe that Jesus took our punishment by dying on the cross for us.
2) Most Xns believe that God is a loving God.
3) Most Xns would argue that we should lock up and throw away the key for any father who would kill their own son as a way of settling a score with an independent third party who was unable to pay up.
4) Most non Xns just don't get the whole God is a loving God but kills the innocent Jesus instead of us thing.
Let's face it the whole substitution analogy is actually a really bad way to explain how Jesus death bring us back into relationship with God. It's time for a new analogy.