Pit bulls have been bred for their "aggressiveness" towards dogs, not humans. In fact, breeders that fight their dogs usually kill the ones that are aggressive towards humans. This has created an extremely loyal and loving dog, but one that is prone to problems.
When selectively bred for "aggressiveness", what you actually end up with is a dog with a LOT of instinctual drive. Pit bulls are not "mean"; dogs cannot think that way. They're not doing what they do to be "mean." They're doing what they do because that's what instinct and handling tells them to do.
So you've got this dog with an unending supply of drive and focus, and they are expected to live like a normal house pet. Unfortunately, this is a road to failure and ultimately violence. When a dog cannot appropriately release his drive, it's going to spill out in other areas. In the pit bull's case, it might come out as prey drive directed towards humans.
Dogs that have this level of drive need lots and lots of exercise, and they need a JOB above all else. They do NOT need a "firm hand", harsh training, or any of that nonsense. All they require is a proper outlet for their prey drive, and enough mental challenge to keep them occupied. This might mean four hours of exercise and play a day, but that is the responsibility of owning that type of dog.
Canines are a serious interest of mine, and banning an entire breed is the most laughable thing I've ever heard of. It is the epitome of completely misunderstanding the issue, the problem, and a really bad attempt at solving it. More people die from lightning every year than dog attacks.
Now I'm not trying to downplay the tragedy of dog attacks, but it truly is a case of misinformation and bad ownership. While I don't agree with many of his methods, Cesar Millan does a wonderful service to the pit bull breed. He has many pit bulls that were used for fighting living together peacefully. The simple fact is that they are getting the exercise and mental stimulation they need. They are not "mean" dogs, and have no desire to fight any longer simply because their drive is being fulfilled!
The bottom line is animal cruelty charges need to step up. People need to go to jail for a LONG time for abusing animals. As always, it's the human's fault, and the dog is caught in the middle of it.