Obviously it’s both the breed and the upbringing. Border Collies are wonderful, intelligent dogs but they will herd what ever they can, even your kids and they will often get a little snappy if they can’t get enough exercise. They were breed to their herding skills and connections to their owner. This is hardly controversial with most people.
Why then would anyone think that a breed that was bred for fighting and protecting people/property (bred for aggressive behavior) will be anything other than aggressive. Put them in packs and you are asking for it. Then you go and train them to protect yourself and incourage aggressive behavior.
Don’t recall anyone ever getting killed by a border collie