Always.
Its always the owners. Dogs do what they know and are allowed. If you think its funny to tease your dog as a puppy, don't be surprised when he grows into a big asshole. And even then, the dog can still change and be good. Every dog
wants to know how to behave properly. The pack mentality is deep.
I currently own a pit. He was a rescue he got returned 6 times before we got hime. He used to get weird around people like others have described. He never bit anyone that I saw. But I have seen him get weird and inch up on people like shit is about to go down. But I fixed that bad behavior immediately (by poking him in the shoulder and redirecting him to behave the way that is acceptable). And now, he is the world's fattest-cuddle-sausage. I take him everywhere with me, and he meets dozens of new people every week. He LOVES people, is totally well-behaved around all people now. And unless I told someone, nobody would ever think think he was anything other than super-loving his whole life.
My dog was the same way with dogs. He used to be an asshole towards dogs, and now he is great with all dogs of all sizes.
He gets a lot of compliments. People without dogs say what a happy dog he is. And people with dogs say 'Wow! My dog usually hates other dogs but he sure likes yours!'
And just a thought--what if pit bulls acted like all those little yappy, bitey small breed dogs? I love small dogs, but
so many behave incredibly badly. Large dogs could never get away acting the way small dogs do.
Every dog should be good with people and dogs. If its aggressive with either, the owner needs to fix that ASAP (and not by beating the dog or punishing it, but by using positive reinforcement and showing the dog the proper way to behave)
If someone is avoiding pit bulls they are missing some HUGE LOVE. Yes, pit bulls might have more attack statistics than many breeds, but think of every insecure, trouble-loving small dick fool you know who is a bad dog owner. They probably own a pit bull or a few. I feel sorry for everyone who has had bad experiences with pit bulls. On the flip side, nearly every good dog owner--like many on this thread--who own a pit bull falls in love with their adorable square heads and wants more pits forever. That must be for some reason. I wish that everyone who has had a bad experience with pits could meet mine so he could change your mind. And I wish I could meet your dogs so that I could give them some of this human beef jerky I picked up at Costco today just for dog treats!
And for those unfortunate folks who ever have to break up a dog fight, I've never had to use this trick myself, but I've heard it has worked successfully many times--stick a finger up the dogs butthole. Get them into a different state of mind real quick.