It all starts with the Christian belief that God created animals (dogs are animals) to serve humans. People that feel dog fighting serves humans a purpose of entertainment think its ok to kill them as part of the show.
Christians don't think that in the relationships between dog and man men are supposed to treat them by human laws of basic dignity. Man is above dog hence a man can kill a dog if that suits his purpose of entertainment.
You will not hear the Pope denounce dog fighting. No sir. The attitudes of many posters on here that man is above dog is very evident even when it comes to cruel death.