What is the point of this debate?
It makes no difference whether the family is to blame for keeping a dog that they have bred to be vicious, what sort of life would this child have had with them anyway? The sort of cretin that is able to 'train' a dog as an attack dog, ie kicking it, forcing it to fight, treating it cruelly in order to make it as fearful as possible, and so on has no business having charge of a child in the first place.
IMO Dog or no dog the child would have grown up to be a nasty little bugger at best with these guardians.