I will not tell you the breed was used to pull carts because that is FALSE and I am not a liar. Although they definately could pull carts. I do know the American Pit Bull Terrier's past. They were bred for bull baiting and dog fighting. Most of these attacks on humans are by badly bred pit bulls bred for money by backyard breeders and NOT temperament.
But what about all the other dog attacks that are not pit bulls? I believe ANY dog can be dangerous in a certain situation. On the dog board I belonged to one person told a story of a Golden Retriever who tore half of a woman's face off. Pit bulls may be powerful, but so are Presa Canarios (the ones that killed the woman in San Francisco). If pit bulls are banned I believe people may turn to this larger breed.
Here is the book I was talking about. I should order and read it. http://www.fataldogattacks.com/