It isn't the breed unless you have a poorly bred specimen. But we have to remember that our dogs are pack animals and pack behavior is nothing akin to what we see with our individual pets. In many cases pets who would never bite anyone, when out with another dog or dogs, will attack other animals or people. Instinct can take over. This is true of all dogs who are, innately, carnivores. i.e. I am a dog breeder and individually my dogs will play with the cats
but any combination of two of the dogs and they will go after the cat. This also applies to taking runs - any one of my dogs will stay in the unfenced yard but let a second one out of the kennel and off they go!

If people who realize the pack instinct is not extinguished in our dogs there would be fewer tragedies for people and pet owners.