Fighting dogs were developed, bred, and trained for dog aggression; people aggression was not tolerated in the ring. People aggressive dogs were "culled".
Are Pit Bulls Dangerous to People?
Despite the fact that pit bulls were bred to fight with each other, early breeders took pride in producing dogs that were trustworthy and friendly to people. Handlers bathed their opponent’s dog before a match, stood in the pits with the battling dogs and often pulled them apart to end a fight. Any dog who behaved aggressively toward a person was culled, or killed, to avoid passing on such an undesirable trait. Pit bulls typically lived in their owner’s homes, where they earned the nickname “nursemaid’s dog” because they were so reliable with young children. In fact, “Pete the Pup,” the children’s friend from the old TV series “Our Gang,” was a pit bull.
Source: ASPCA: The Truth About Pit Bulls
The problem is now the majority of these dogs are no longer being bred for what the breed was developed and those traits that were highly selected for (dog agressions and not people agression) are no longer under strict selection. When you stop selecting for working traits, these traits are lost, altered, or not well balance within just a few generations. This also happens with gun dogs, herding dogs, and livestock guardian dogs.
Herding and flock protection are not the same function and require different breeds/dog; for herding you want the livestock to move away from the herding dog which is opposite to what is desired with a guardian dog.
