Pit bulls are also bred for shows.
Here is the AKC breed standard for the American Staffordshire Terrier.
http://www.akc.org/breeds/american_staffordshire_terrier/I can't find the guidelines for how much aggression a dog can display w/o being disqualified. I do however recall watching a dog show on television some years back and the commentators talked about that for awhile. There is a limit that cannot be crossed for show dogs. Breeders that breed the show dogs know this and won't breed dogs that are overly aggressive.
Some information from this link:
http://www.goodpooch.com/MediaBriefs/GPpitbulls.htmAre 'Pit Bulls' Naturally Aggressive Towards Other Dogs?
The short answer, "No."
"There is no scientific proof that genetics cause a breed of dog to be aggressive, vicious or dangerous." - testimony from Standing Committee on amendments to the Dog Owners Liability Act. 2005
"Variability in behaviour has a wider range within a breed than between breeds. Within the discipline of psychobiology and animal behaviour there is no data from empirically supported studies, published in refereed scientific literature, to support the idea that one breed of dog is `vicious.' The adult behaviour of a domestic dog is determined overwhelmingly by its experiential history, environmental management and training." - Dr. Mary Lee Nitschke, Ph.D.
Believing the myth that 'pit bulls' are naturally aggressive towards other dogs, all-too-many people restrict their 'pit bulls' from normal, positive, social interactions with other dogs. Here's an example of how it all starts:
The proud owner of a little, 9-week-old 'pit bull' puppy was out walking her new family member when she came across another person walking her dog. The other dog owner understandably stopped to meet the tiny puppy. She asked if it was okay if her dog "met" the woman's puppy, and the woman agreed. The older dog got up and walked the few feet to sniff the puppy, at which point the puppy's owner pulled up on its leash so she was essentially hanging the poor little thing, with just its two hind legs on the ground.
The owner of the adult dog asked the woman to "Please let you puppy's leash go.", at which point the puppy's owner did nothing. Seeing the poor puppy strangling at the end of the leash, the other dog owner thought it best to move on.
This is indicative of the anxious responses many dog owners exhibit when meeting other dogs. By pulling tight on leashes and collars, or worse (as in the case of the puppy's owner), these kinds of inexperienced dog owners are actually creating a negative association with meeting strange dogs. How would you feel if every time you met someone new, someone yanked a collar around your neck; harshly pulled you away; and ultimately never allowed you to interact with strangers? You wouldn't exactly be nice and relaxed around strangers, huh?
Same goes for dogs
From further down in the article:
There are two main points that many people fail to recognize:
1. There is no such thing as a breed of dog that won't bite.
2. The breeds at the top of biting statistics are the most popular breeds at the time. Meaning, in Canada, Labradors, Golden Retrievers, and German Shepherds and other popular breeds top the bite statistics. Any dog can bite. Any poorly trained and unsupervised dog may bite unprovoked. Breed is not the deciding factor, training and supervision is.
Proper training of any dog includes lots and lots of socialization with as many humans and other animals as possible at the earliest possible age.