Because after all, it is almost certain that an otherwise normal person exhibiting this type of behavior experienced a great deal of childhood trauma, childhood trauma that actually impairs the normal development of the brain and can cause permanent damage. So in either case the child rapist is probably suffering from some sort of brain damage that was beyond his control.
How child abuse and neglect damage the brain
Don't get me wrong, I am also disgusted by this type of behavior, but I think it's best to look at the big picture than to work ourselves up in a vengeance fury. Of course if it was the parent of the abused child doing the attacking we would probably sympathize with the violent reaction because we might understand why a parent would react that way. What most of us can't understand, however, is why this bloody butted fellow behaved the way he allegedly did, and I would argue that is because our brains were not broken in the same way that his probably was.