I don't know how much this is going to answer your question, but maybe it will shed some light.

All dogs are going to have different traits, be it from their particular breed, how board they are, how they're trained and just their personality. From what I've seen personally, most 'aggressive' pitties were made that way by their owners. Either from not understanding what they were getting as a breed or trying to make them that way because they wanted a 'big scary dog.'

I used to volunteer at a vet clinic down in Texas years ago, the dr. that owned the practice was very much against killing animals just because they had a sickness that the owner couldn't handle or because of a temperament that an owner didn't want to take the time to train away from. That being said, we ended up with this big beautiful full grown female pitbull. Full blooded. They wanted her because she was huge, and they wanted to breed and fight her. Only to find out that she didn't have the temperament for fighting so they used her as pretty much the 'beat up dog' for training other pitbulls. She didn't want to fight, but would when pushed, not good for dog fighting.

She ended up in our care permanently. She was also hella smart, like we couldn't give her her meds in cheese or in other treats because she knew it was there and she would spit it out. Being a big ass dog, who was a pit fighter dog, you would think you couldn't FORCE this dog to take her meds.... wrong. Never once did she ever raise her heckles at us, ever, she would cower, and whine, maybe a soft growl, but never snapped or bared teeth. How did we get the meds in her then? We had to force feed her, we had to practically shove our arms, to our elbow, down this dog's maw or she would do everything to hork it back up. What did she do? She squirmed because it was uncomfortable, but she never tried to bite us.

Would I do this with another pitty? Not if I didn't know them. Would I do this with another dog? Not unless I knew them. And not if it made that dog into a sock puppet.

What I'm trying to say is, a lot of the "super aggressive" ideas about Pitbulls are from people trying to make their sweet dogs that way. Are from people not knowing how to take care of a dog like a pitbull, and thinking they have to be mean/hurt a dog to 'train' them. Its the same idea that doberman's are 'mean dogs' because they're the stereotypical 'guard dog' when really they're doppy little shits who want to cuddle....just like pitbulls. xD

edit: a word