I've been the owner of an American Staffordshire Terrier (american pitbull) for almost 8 years, until she died because of a spinal stroke (common problem for the race). My dog was as sweet as honey, playing peacefully with kids and even cats. The problem is not about the race but the owners. Having a pitbull or a rotweiller as a pet requires responsibility and a certain knowledge about dogs. They are not natural born killers but they can become dangerous if not handled or educated properly. This is true for any race: in my native country, Italy, some years the dog that jumps on the top of the blacklist for attacks to humans is the German Shepherd...
A dog is not a weapon. Is a friend and a companion, an intelligent creature that can become so important to be at the same level as the other members of the family. They have instinct, indeed, but they will never do anything to displease the owner. They learn it when still cubs. A dog will always suppress it's istinct if that means getting praises and attention from his god, the owner. Any dog. Once again, the problem is not with the dogs but with the people thats educate them.
That's what I'm saying, the owner isn't always around so these dogs will follow their instinct first. If you read most of the pitbull attack stories it usually begins with either the dog escaping from the owner's home or the owner not being aware of what's happening.