It’s not the training, it’s the indiscriminate breeding.
More to the point I think it the “discriminate” breeding by human animals to create hostile, vicious lines to assuage their need to be macho.
It’s both. Training and lack of proper training are a major part of it.
Breed specific laws are quite racist if you think about it. If someone is willing to segregate a single breed of dog for restrictive laws, they’re willing to do it for certain classes of people too.