The pitbull decscended from a breeding mix of a Bulldog and a Terier. Many breeds of pitbulls are mistakenly labelled as pitbulls by origin. Breeds like the American Pitbull Terrior and American Bully are essentially similar dogs that should be given a different breeding catagory.
Unfortunately, many pitbulls were originally bred as fighter dogs. These fighter dogs were crossbred from bull baiting dogs like the bulldog. Due to the origins, the current stigma around a pitbull is aggressive and fierce. This makes for a very good source of protection for an owner.
However the dogs temperament ratings are inclusive of self protection and owner protection as well. Based on these ratings, the pitbull is not aggressive in most of it’s breeds. Pitbull aggression and the need to walk with a muzzle is strictly a condition of treatment by the owner.