Pitbull terriers are a type, not a breed and many many thousands of dogs that could be considered 'type' live harmoniously in happy families. It is the fact that morons like to get hold of these types of dog and use them as status symbols and weapons that give the type a bad name. Valhalla will know more about the attacks preceeding the DDA than me, but one thing is clear, the DDA hasn't actually done much good and healthy, well socialised dogs are being put to sleep as a result of it.
Obviously a big dog is physically capable of doing more damage than a toy breed, but any breed of dog if raised incorrectly has the potential to do huge damage. That even includes my lovely Golden Retrievers. Some breed are more reactive than others, but this also includes a lot of breeds that are not banned.
What would help are stricter laws regarding dog breeding and owning. More than just a dog licence, which is useless in the form in which it exists in NI.