Staffordshire bull terriers were bred for fighting, that's what they are pre disposed to.
Personally I would class every dog as a dangerous one, even those family pets that have never shown any sign of aggression could potentially do somebody some serious damage. Yes there is a lot to be said for how dogs are treated and cared for but I wouldn't have a St Bernard and expect it to be a good rabbit catcher, nor would I expect a chiwawa to enjoy a daily ten mile hike or a springer spaniel to spend all day content in a house.
Certain dog breeds have certain characteristics that are present across the entire bread, all bull dogs have higher levels of aggression imprinted in their DNA, that's not to say all will act on it but all will have that potential to far easier than Labrador, it's not their fault it's just one of those things which is a problem only compounded by the fact that they are a status symbol for many who train them to be overly aggressive.
We have a collie, and they can be a funny breed, you either get a good one or you get a complete twat, one of our collies litter is very aggressive and another is just like ours - both stayed on the farm and were raised the same. I've always cringed when people let their dogs play with babies and jump up toddlers, it only takes a spilt second, a poke in the eye a pull of a tail and it's too late and that's any dog of any breed.
We had ours as a pup and for almost three years before eldest child arrived, we distanced her from him, he's never been funny with the kids but has snapped at other dogs in the past, he was overly coddled by my husband who took him to work and has always been content with his own company. It's a shame in a way because the kids absolutely adore him now, it's only in the past 12 months he's been more interested in them and now youngest is older and knows how to treat him we're not forever telling them to leave him alone. Unfortunately he's now hit his 13th year and we're not going to have him forever.
I would never have another collie, mostly because we'd never get another Jeffery, he's an absolute star but also because a collie isn't a breed I'd have necessarily chosen with young kids, if the kids had come before the dog we probably wouldn't have had him. I've been looking for a pup, on and off and I'd be happy enough with any medium size breed or cross breed but I wouldn't consider any bull dog type, not because they're all dangerous but because many of them can be.