I can understand the side of people who disagree with it. As a fighting breed, ANY human aggression was completely undesirable, and ANY dog showing ANY human aggression was culled, and it's genetics removed from the breeding lines. After all, the handlers had to enter the rings with the dogs, separate them, prolong the fights, treat the wounds to ensure their assets survived, etc... Something that couldn't be done with a human aggressive dog.
HOWEVER... the days of fighting are long behind us. So now you have this very versatile, intelligent, and athletic breed. What is to be done with it? The APBT was the ORIGINAL dog hero in America, because of it's drive and versatility. The first breed awarded war metals. If you want to go out, do proper bite work, enjoy schutzhund, then have at it. I mean, you're not planning on fighting your dog, are you? So does it matter if the dog is "encouraged" to bite humans in appropriate situations? No.
EDIT: Protection does not automatically mean human aggression. In fact, a dog with severe "aggression" issues is the least suitable for the dog.
BTW, Dobermanns were NOT bred for "human aggression". Instead, they were bred to be strong willed, intelligent, and ALOOF with strangers, NOT aggressive. An AGGRESSIVE dog is not going to be able to differentiate between threat and non-threat.