This seems to have taken the best dog to protect your loft to the best fighting machine :( :(
Pitbulls are banned because they are exactly that, pitbulls are like lurchers they are cross bred for a purpose and the mixes are numerous, they are mostly bull crosses bred to do a certain thing fight, problem is not all the pups in the litter have got what it takes so they are sold off as pets or guard dogs with the inbred fighting instinct, some make cracking pets but in the wrong hands can be a time bomb waiting to go off
Dog fighting can be done in weight categories so they breed the dogs to fit the category the same as pedigrees are bred to a standard.
It is as complicated as pigeon racing, winning bloodlines changing for vast amounts of money, good breeders producing good stock, back garden breeders, organised stud farms selling as much as they could :-/
It's not the dog in the fight, it's the fight in the dog 8)