It's the owners who are at fault the majority of the time.
Every fucker gets a dog, that's the easy part, but raising a dog to have a good temperament is another thing, and so many people just aren't educated or are a waste of space.
Unfortunately, it's certain breeds of dogs that end up destroyed and in the media. If its large or strong jawed and not always placid (i.e rottweiler, alsation, bull mastiff, staffie etc) then there is the potential to do serious harm, and in the wrong hands it happens.
A Labrador could be dangerous, but thankfully they're usually so laid back and sweet natured that it doesn't happen.
A snappy little terrier is only not dangerous because it's small.