I have to disagree too. Every breeder knows that you have to breed for temperament, and you should never breed an aggressive dog. Pit bulls have been bred for their aggression. That will not change.
I have also found that little dogs, can be the worst. The owners are more willing to accept bad behavior, because of their size. Every time I go to the vet with one of my dogs (mastiffs) some little dog is trying to attack them.
I think people tend to think protection and aggression are the same thing. They are not even close. You do not want your dog protecting you from friends and family. That is just aggression.
A protective dog will be able to sense real danger.
As much as I love my dogs, if I ever had one even growl at someone, it would be taken to the vet and put down that day. My dogs are to big to take the chance of someone getting hurt or killed.
Thats more than a little extreme. You need to learn to train your dogs and probably change some of your own behavior also. Dogs take their cue from their owners. It's the human owners responsibility to be the leader of the pack and to stop unwanted behavior immediately as it occurs. This works for all breeds. Your dogs will love you for it.