I see a lot of people here are putting out that line about " it is not the dog, it is the owner."
While there is some truth to that, just look at many of the people having bully breeds, it is not the whole story.
These breeds, pits, Staffordshire, and American bull dogs are all extremely powerful dogs with a fighting style (not all, many) that is unique among dogs. Too many bullies (terriers in general) are animal aggressive. All bullies must be kept under control at all times. No loose dogs and it is a rare pit that does well in the dog park.
I have worked with hundreds of pits, though the ones that are in shelters are, generally, the worst of the lot, or having companions not suited for such dogs. I take a firm hand with any bully knowing that in seconds a poorly handled dog can cause havoc. Some dogs bite more often than bullies but the way bullies attack and hold on can be devastating.
From a young age these dogs must be well trained, attentive to the leash, socialized with other dogs in a controlled enbvironment and not used as a weapon which too many people do.