I don't think it is quite that black and white. You may find this study interesting:
http://www.dogbitelaw.com/Dog%20Atta...%20Clifton.pdf
Although there are certainly very nice pit bulls that are very calm, the data does show that there are inherent problems with the breed. Certainly bad owners and bad breeders add to the problem, but if you look at the facts the number of serious dog attacks causing death or permanent disfigurement are overwhelmingly in the camp of pit bulls, rottweilers, and presa canarios, and of the three pit bulls are responsible for another disproportionate share. These breeds are able to cause much more harm. If a collie, poodle, or other breed has a bad moment they snap and bite, but don't maul. The potential damage from a pit bull is off the scale. And when you take the population of the breed into account - something less than 1% of all dogs, the numbers scream even louder.
Again, there are bad breeders and owners, but looking at the numbers it is difficult to argue that all these very serious attacks are the result of the owner/breeder. In fact, the author found that in 2/3 of the cases, the death or disfigurement of the human was the first time the dog ever showed an aggressive attitude, so it is not just dogs bred to be mean or to fight.
The "its the owners, not the breed" mentality is shared by many, but it is only fueled by emotion, there are no facts to back it up whereas the facts in the link tell a pretty convincing story. I know several pit bulls and I really like the dogs, but as I told my sister in law, with grandchildren around, why on earth would you take this risk based on the data? Children poke and grab ears and pull tail, its what kids do, and that is a bad combination with certain breeds.