Finally something I can't argue with BO or GA on.
Every breed has certain traits. It is these traits that are developed and enhanced through breeding over generations of animals. (Staffordshire?) Bull Terriers were chosen for their natural strength, speed and aggresive protective nature, not for their cute cuddly friendly personalities. Breeding further enhanced these traits and at this point it is in all of them, like it or not.
Sure some idiots train them to display that nature more than others or to bring it out on command but it's still in there somewhere in all of them. Others have one they think is the exception to the rule until it's too late. Yes any animal can snap, but if and when these guys do it causes a lot more damage than when a bichon frise loses it's mind. Most of the people I know who have these dogs are dirtbags and chose the dog to be, or appear to be, tough guys. Just look at the names their owners give them. Nobody names their pit bull rover, fido, fifi or anything like that.