The pit bull dogs that turn aggressive have most likely been trained to fight and be aggressive.
I've had a pit bull dog that I've raised from a puppy and he was really gentle and even gentle around kids.
He was never trained to be aggressive or fight but was loved and he loved people all the time until he died of old age.
So while Pit Bull dogs can be aggressive and are most likely to be mean towards people some pit bull dogs can be very loving as long as they haven't been trained to fight or be trained to be aggressive.