Hi CS,
Sure, they were bred to be good fighting dogs, but they have to be trained to fight. You don't just get a pit bull pup and automatically have a fighting dog.
Actually, what has unfortunately happened is a small but prevalent group of people have pre-selected the pit bulls that were the most aggressive. They roll the pups and young dogs and keep the ones that are the most agressive and cull the non agressive ones.
Unfortunately, the whole breed has been corrupted. I realize thats not the same as saying "every pit bull is a bad dog," but the line is completely out of the control of responsible breeders and owners. These pits are in fact genetically aggressive fighting dogs.
My buddy has a border collie. The very first day of puppy class, she instinctively herded the other puppies into a corner. No one had to teach her this behavior, it was genetically encoded in the same way that aggressiveness towards other dogs is encoded in pits.
While MOST of the pit bull incidents could probably be mitigated by responsible ownership, why keep a human created failed breed around that is essentially a ticking time bomb? We wouldn't perpetuate a breed of labor horse that was genetically predisposed to have faulty knee joints, so why should an aggressively wired dog breed be cultivated?