A well trained and properly socialized guarding breed is less likely to be involved in a predatory attack than an un-socialized, untrained dog of any other breed. Rules are often broken and safety plans can and do fail. As a trainer who offers group classes along with a myriad of other services, I instruct my trainers to inspect leashes in novice classes, routinely, as many people will bring an untrained dog out on a frayed leash. They are obeying the letter of the law even if they fail to observe its intent. I will say, however, that when they finish classes, they are more educated on proper care of equipment, as well as proper handling of their dogs.
Muzzles can and do fail, as well.
Just ask any veterinarian who has been injured while treating a muzzled, wounded dog. Try just walking a dog that is quite friendly, yet pulls, on one of these leashes for a weekend. Then you will see what I mean. Give people a false sense of security and another reason not to responsibly train and socialize these dog. Breeders will say that everyone has sold at least one puppy to a person whom they wished they hadn't.