[SampleMan]

It is self evident that dog breeding has resulted in a vast number of breeds with greatly different traits. Traits that make them innately more prone to retrieve, herd, lock up on game, track, etc.

So I wonder why it is, in your opinion, that dog breeders who have spent the same amount of effort to create breeds to be innately aggressive killers have failed.

There are many aggressive breeds, but only a few that have also been bread with the strength to kill other large dogs and people with ease. Interestingly, none of these were intended by the breeders to be family pets.

Perhaps its not wise to expect retrievers to stop retrieving and herding dogs to stop herding. I believe the term is tempting nature.

[MAD-AS-HELL]

Am Staff back long ago, prior to the 60/70’s were one of the most owned/popular family dog and there wasn’t an issue. What seems to have happened is that scumbags started to breed the dog for their fighting aggressive traits. The other problem is you are always going ot read about the problem dogs and not about the dogs that dont’ have problems. It’s just like gun crime. It’s always the negative stories about how a gun was used for crime you read about but not the ones where a gun was used to stop crime.

[LongElegantLegs]

But you can channel a border collie's drive into flyball, or agility.
A lab can be subverted from retrieving to drug detection.
If you have the time and the will, you can use them for whatever purpose you want.

Pits are no different.

[SeeSharp]

So I wonder why it is, in your opinion, that dog breeders who have spent the same amount of effort to create breeds to be innately aggressive killers have failed.

The failure is not in your logic but in your premise. A fighting dog that exhibits human aggression is useless and will be quickly destroyed. Fighting dogs have to be handled by strangers during fights and often have to be handled while seriously injured. Docility towards humans is a must and is just as important as fighting spirit towards other dogs.