Well you could have asked me, since I was the one using that argument.
Dogs in general do trust and serve people in general. "Guard dog" is a specialty that builds on the dog's natural tendencies to protect his pack, his family, is master. He will defend that master to his death without question... Are you telling me you don't recognize the responsibility that master has to treat that devotion with respect and returned loyalty? That is the trust, that is the contract.
Owning an ordinary pet or a guard dog isn't the same as raising dogs for food. If those dogs trust the farmers (or whatever you call them) raising them, then so would pigs or cows.