You often hear people say "Dogs bred for aggression towards other dogs aren't necessarily people aggressive" and that's true BUT:
take the Border Collie. Bred to herd sheep. In the absence of sheep, a Border Collie will often take to herding other things - people, bicycles...moving things will trigger the herding instinct and cause the herding drive to be directed onto things that are manifestly not sheep. Sometimes they will nip at the heels of children in an attempt to direct them.
A dog bred to retrieve game will often retrieve socks, and greet every visitor with a mouthful of shoe, or whatever it can get hold of. The drive to do what it was bred for is hard wired into its very being and in the absence of an available duck, anything will do.
There are plenty of other examples of dogs being bred to have certain traits, which will be redirected onto inappropriate items, or inappropriate ways (BCs can be terrible sheep worriers if not trained properly - herding drive is modified prey drive after all).
A sighthound bred to chase small furry things - especially if it's had some success, with all the resulting excitement/adrenalin rush, won't NECESSARILY be a danger to someone's small fluffy chihuahua - but predatory drift can happen - again, a selected trait being inappropriately directed.
I'm not saying that a dog that has been bred for aggression to other dogs is more LIKELY to turn on a human - but to me it makes sense that IF that aggression is triggered, for whatever reason, then that hard wired urge to bite, hold on and shake is more likely to kick in than in other breeds.
I wonder if denying this is as naive as saying "Well yes you've got a working Collie from a long line of working dogs but it's no more likely to try to herd your kids than a Lurcher is".
I promise I'm not in favour of BSL. That's not my point. I think the main thing to target is irresponsible breeding - that with ALL breeds but especially those which have a history of being bred for aggression it's SO important that those traits are bred out.
I hope all that comes out as it's intended. It's late and I'm tired :)