It's not about training your dog to attack people... This is sports training, not protection training. I would not be confident in a dog to protect me from Sch training alone.
We work the dogs in prey - ie they want the toy. A person then holds the toy (a helper) and if the dog is confident enough, it learns to take something from a person on command. Again, you will find that 99% of dogs will lose interest in the person entirely once they have the toy. To get a dog to be protective, you have to tap into defense drives (ie make the dog feel that it's in a threatening situation). Schutzhund doesn't do that, it teaches the dogs to respond to their handlers even when in high prey drive and it's all about play. That's why people like Nekhbet talk about other sports like French Ring etc because from Schtuzhund alone, you can't always know how that dog would stand up in a real situation. You know that the dog is trainable - that's essentially it. French Ring leaves little doubt.

There are also 3 components to Schutzhund, Obedience, Tracking and then Character work - everyone seems to forget about the other two. You can't even start training the Character work until you have a BH, which means that you have a dog that is quite obedient, at least if you're working with an ethical club. There are a couple of different camps in the Schutzhund world - those who are Sch athletes who buy dogs for the purposes of the sport and then on the other hand, those that have dogs that are pets who think their dogs would enjoy the sport but the dog is a pet first and foremost. My dog is still a pet first and foremost and the sport is very much about painting a clear picture for the dog - if he walks onto a field with blinds and someone in a bite suit, he becomes visibly excited but without those features he's just his normal self because he is socialised beyond Schutzhund. I don't believe I have awakened anything within my dog through taking part in that sport, he was always very high drive. All I have done is achieved a much greater degree of obedience and reliability when my dog is in drive. I can call him off a cat now (ie a true distraction recall) and I couldn't do that before our training so I think it has actually meant that I have a dog that is much less likely to attack or cause damage to another person or animal.

If you have a dog with the genes that would make it good at Schutzhund, natural drives etc, then your dog will be safer once you have worked with the dog in those drives.
99bottles is totally right. If you have a reactive dog with a lot of prey drive then Schutzhund is a good place to start. For one you have trainers used to handling highly driven dogs and a big toolbox to help your dog channel that drive into productive exercises. The ANKC will not recognise Sch titles, even the BH which is simply 'traffic dog' test (basically heeling and not reacting to stimuli, every dog has to pass BH before moving onto SCH titles) In these sports you reward dogs for self control, teaching them it's more rewarding to not randomly react and find their own satisfaction. The point is to make bombproof dogs, not backyard, stick poked attack dogs. The ANKC will not kick you out but the SCH title will not be on your dogs pedigree and you can't be a member of the GSDC because they're staunchly against it too.

This video is a good example. A dog in public, lots of distraction, has prey drive but all it wants is attention and reward from it's owner. And it's having a blast doing it. We need to resurrect the sport, especially in Victoria where I am. We would have a lot less problems if these working breeds had a proper outlet available to them on a regular basis.