I was walking my dobie/shepherd cross on a 6-ft leather leash at my side when 2 miniature schnauzers attacked him. He laid down in the middle of the campground road cringing until the woman was able to get the two dogs off him and in her trailer.
Any dog can attack. Any dog can injure. Yes, a larger dog will do more damage, but that 1) doesn't make it less traumatic to the victim; and 2) doesn't mean the breed is bad or evil.
Very few "dog attacks" have happened simply because the dog was crazy/dangerous/etc. The majority happened because someone made a mistake.
Had the woman in my example kept her dogs on leashes and under control, my dog would not have been put in a position that easily could have led to his protecting himself by attacking back. Trust me, he got rewarded all weekend for his behavior, but I would not have blamed him if he had reacted differently.