I agree it is all about upbringing.Certain breeds attract the wrong type .I've had 3 Rottweilers,one of them was a rescue dog that a nice human had decided to beat up and burn with cigarettes.
He was different from the other 2 and even when he had learned how to behave and become the most loyal and obedient dog we have ever had I was always aware of keeping an extra eye on him.But that would have happend with any dog with that upbringing.
One of our Vizslas is a rescue and she is very uncertain in the vets,she is the only one of our dogs we have ever been offered a muzzle for in the vets.I should add its not needed she is fine once she is reassured.And out the vets :

We put up with a lot with our Rotts,an old man tried to hit them with a walking stick,my wife got spat on a child hit one of them over the head with a stick.
One of them ended up with a torn ear when a Lab went for him .
With these dogs because they are so powerful and combine that with the macho types wanting to strut around then you have a deadly combination.
And any dog brought up in the "wrong" way has the potential to do a great deal of damage.
Here in Scotland the Government is in the process of moving away from breed specific legislation to dealing with shall we say untrained owners.