Humans have selectively bred dogs for thousands of years. Dogs have been bred for different uses e.g. sheep herding, hunting, racing and, sadly, for aggression
It is not in any way the fault of the animal. Mankind has bred dogs to have large powerful jaws, aggressive tendencies and strong defensive behaviours.
We have created this problem and the way to minimise the risk of serious injury or death is to prohibit certain breeds of dog identified as dangerous.