My manfriend has a pit...and it's a puppy right now, and it has puppy ways, but he's training it to be a killer, guard dog...You can't pet it and he won't let it close to you and keeps it in a small cage, big enough that it can turn around in...while being left in the garage....sometimes he'll take him for a walk.
Not all dogs are dangerous...and it's the owner that makes them like that.
Generally, dogs are much like their owner's personality.
For example...
I had a cocker spaniel as a child, and I'm sure the dog would have turned out okay, but I abused it, threw it across the room, pounded it's paws with my fists, and hit it with pillows...and the vets called him a blonde rottweiler...he tried to attack everyone, except me...then one day he decided to try and attack my dad and that was it and they put my puppy to sleep