@MyDogTails
The issue is that no-one thinks their dog is capable of attacking a seal or deer or sheep or human. But they're wild animals whether we like it or not and it frankly isn't down to training, it's instinct.
The smaller the dog, the less likelihood that an attack will kill.
I have a retired greyhound. I know full well that he will chase and kill anything he can catch (squirrels, rabbits, rats, cats, small deer, foxes, hedgehogs, badgers). This is why he is muzzled on walks. Having known him many, many years, I know he poses no threat to other dogs and humans, though I still worry he may go after a toy breed (but he never has) as the chase instinct is so strong in sight hounds.
Dogs look different because they are bred for different purposes. The bull breeds are fighting dogs and my breed is a racing dog. My dog was retired because he was slow but it doesn't change his breeding or his nature and you're going to stand a far better chance if he bites you with his pointy-faced jaw than if a bull breed does.
Don't assume owners don't know their own dogs. I chose my breed for their famous laid back disposition (indeed, he spends the majority of his life asleep) and affectionate nature. However, I'm not blind to his faults and spent yesterday blocking a gap in our hedge to deter next doors new cat from using our lawn as a toilet (no issue picking up a few more poos as dog does plenty of his own, but he will kill the cat if he gets his mouth on it). The muzzle on walks is a precaution too (you'll see many sight hounds muzzled in public as it's common with dogs trained to race).
I'm going to play Mumsnet bingo now. 100 points for any poster who tries to explain that bull breeds jaws don't really lock (yes, we know, it's an expression) and 200 points every time I see the words "Nanny Dog"!