They are inbred to fight. It has gone on for so long that even if one appears to be a warm and loving pet, they have a history of snapping and reverting to their pre-ordained killing machine status.
Outlaw the breed. Period.
My ex-hubby tells of growing up in the 40s with a pit bull as a family pet. Tells of one time he toddled off too close to the arroyo near his house and fell in, whereby the pit bull jumped in after him and dragged his scrawny soggy diapered butt back to his mother, where she promptly tanned his bee-hind for wandering off.
Obviously the breed has changed since the forties.