Wow, let me tell y'all a story if you think all pit bulls are mean and bad...
My neighbor found a rott wondering the neighborhood (country neighborhood), and assumed it was mine because I had a pit and a boxer. He literally tied it to my tree and left. After much looking, there was no owner to be found. When I tried to integrate him into my house, he was very dog aggresive. I put a muzzle on him to avoid a pit/rott/boxer fight. He pushed my pit against the wall with his head (because the muzzle was on), growling pressing his dominance. My pit never once lashed out at him. He looked at me terrified, not knowing what to do. And guess what, I got him out a shit hole that 'he wasn't cut out for fighting' (needless to say, I put a stop to that sh*t). You know how they come to that conclusion? They have to teach a dog to fight. Yes, you can inbreed to make dogs more aggresive. But dogs don't fight by nature. They assert dominance, and some house dogs are very aggresive because its their house, reguardless of the breed. My mom has an english pointer that is the most spoiled, hand fed, babied dog ever. And guess what, she's very dog aggresive in her own home. Outside she's fine, but bring another dog in her house and see what happens.
Dogs don't fight for fun, thats a behavior thats taught to them.