I really like most dogs and often dogsit for my friend. They are great company on walks. However, I think the onus is on the dog owner to protect the public, although obviously sensible parents will not leave a very young child alone with a dog. My daughter had a lovely, gentle springer spaniel, but she developed a brain tumour and turned vicious overnight.
In New Zealand, every dog has to be microchipped and registered with the council every year. If your dog wanders, you can be fined and sheep worriers can be shot.