If someone murdered someone out doesn't mean I automatically wish the the murders death. I don't know the circumstances, mind set, mental history or anything. The dearh of the dog doesn't undo a bite. It's there animal abuse by the owner? Has the child teased or activated the dog? Did the dog have prior incidents of violence? Are there other options rather than death? In this situation it seems unlikely this was provoked by the child. But there are still unknown factors. The death of a dog doesn't undo damage. Killing a dog doesn't bring me joy, maiming a child doesn't bring me joy. Both together certainly doesn't kindle any positive emotions.