It's the breed, period.
They were bred to fight, just like border collies are bred to herd. It's in their genes.
It can be glossed over with training but when the time comes, and who knows what sets them off, they revert to their breeding. Fight, kill.
With jaws of a steel vise they do maximum damage and are oblivious to pain.
I agree.
When we were kids out collies would herd us back into the yard if we got anywhere near the street.