An aggressive dog is the result of poor ownership. This is not only true for the American Pit Bull Terrier, but for any breed. A person who does not properly train, exercise and socialize their dog is raising an unstable dog who may turn aggressive.
American Pit Bull Terriers naturally love people and are not instinctively aggressive to people. Quite the opposite, they love to be near their family and at one time they were called "Nanny dogs" because of their gentle way with children.
American Pit Bull Terriers can be aggressive to other dogs, but not if they are properly socialized from a very young age. I began to socialize my Pit Bull at two months- right after I got him and he shows no aggression to other dogs and enjoys making new dog friends.
American Pit Bull Terriers can have a high prey drive, but this is true of many breeds, specifically those bred for hunting (did you know American Pit Bull Terriers have been used for hunting?). It is once again in the training. My pit bull was raised with beagles who taught him to chase after squirrels, but he has never caught one and will not chase them if we are on a walk and I tell him to leave them alone.
In addition to raising a Pit Bull correctly, Pit Bulls can be rehabilitated. Most of the dogs who were victims of Michael Vick were rehabilitated and went to loving homes. Some even went into therapy work.
Also aggressive dog does not necessarily need to be put down, but often times only require an understanding and patient owner who can keep them from situations where they become aggressive.
I have written a hub: https://pethelpful.com/dogs/Where-There-are-Dogs
This hub details the ineffectiveness of Breed Specific Legislation and the benefits of lifting breed bans.
I hope one day all breed bans will be retracted and all breeds will be able to find a loving home.