1) There is no such thing as a "pit bull" breed, but rather a number of breeds which are collectively referred to as "pit bulls". As such we aren't talking about one breed that is disproportionately likely to attack with lethal force. The definition is ad-hoc, which a) feeds into likelihood to misidentify the "breed", and b) creates a situation whereby perceived "likelihood to attack/visciousness" becomes one of the defining criteria of the group. It's a self-fulfilling prophecy.
2) Wikipedia:
Pit bull-type dogs that I've run into in my personal experience have been total sweethearts. Personally, I've had far more terrifying run-ins with Huskies than I have with large-sized bulldogs. At the end of the day, I'd say owner, training, and quality of life are far greater determinants in likelihood of dog attack than individual breed.