It is true that they are often bred to be aggressive -- breeders will often taunt and tease the puppies, teaching them to attack and fight back.
However, show people have a hold on the breed now, and while in alot of cases breeding for conformation can do bad things to temperament, a serious show competitor will breed for good temperament so the dog can be examined by the judge nicely and handled by strangers in the ring without issues. I can see the aggression and drive being bred down.