I just can't get on board with the opinion that this is purely the owners and nothing to do with the temperament of the breed, sorry, but I can't.
We all know Staffies that are soft as anything and not owned by 'chavs', but there are also Staffies correctly brought up who prove problematic and revert to 'breed type' (aggressively) in certain situations.
Lad I know has recently had an 8 week old Staffie, and he's done everything he can to bring it up as a loving family pet, and it is, but age 6 months, despite massive amounts of socialisation with other dogs it is very very protective of it's things. Recently my dog went near a stick the staffie was chewing and it growled, the kind of growl that no six month old puppy should be sending out when another young unthreatening dog goes near it's stick.. Had my dog had any bottle no doubt a seriously unpleasant incident would have occurred, cos that Staffy pup was not for backng down. I don't know another breed that is so aggressive when roused with other dogs.
Furthermore, last week, lady with a 4 year old male Staffie was playing with my dog and a Beagle. Beagle lay on it's back playing and the Staffie stood rigid over it. Beagle was submissive so accepted the dominance, but the minute my dog tried to play with the beagle the Staffie let out a very long low growl to warn him off. Again, my dog is not for fighting and is very submissive so nothing untoward happened and I put my lad on the lead to prevent anything nasty occuring. But both of these Staffies are well bought up and living in loving family environments, yet both have that streak in them for aggression towards other dogs. In the right hands this is controlled, but it's still there and to deny this is just wrong
No doubt the chavs and their ways don't help, but there is no doubt in my mind that this breed are dog-aggressive, more than any other breed in my opinion.