so you DO feel a PPD can become dangerous...
I'm not hunter, but this is a good question and many people do wonder about this.
There are a lot of factors and variables that will affect the end product once you start protection training with your dog.
The training, assuming it is well done, in and off itself does not make your dog more dangerous, but you have to start out with a dog that is suitable and of proper temperament for the work.
IF (big IF) you have a dog good temperament, IF you have good, knowledgeable training, IF you go slow and build a solid foundation of obedience and control in bitework, IF you have full confidence in your dog that you can control him always, and IF you are willing to continue on with the maintenance training on a regular basis so that basis of obedience, confidence in a fight, and control even when working in high-drive, be it prey drive or defense drive is always there, THEN no, the training in and of itself will not make your dog more dangerous, if anything, it teaches the dog greater self-control and builds a stronger bond with the handler due to the intense level of training.
Though the protection phase and the obedience phase do need to be trained together, because if you put too much control on a dog at too young an age, they can become unwilling to work away from you, and not trust themselves to act independently when appropriate, since their early training has drilled into them that the safe thing to do is to stay by your side and wait for the owner to tell them what to do. Absolutely wonderful for a well behaved pet, not so much for a working dog that needs to have the confidence to sometimes, in some situations, make decisions on their own.
That is why when we raise Schutzhund dogs, we always harp on people to just let the puppy be a puppy, and we put up with some behaviours, like jumping on people, that the dog is supposed to be comfortable with at a later stage in their training. We don't want to extinguish those behaviours, but use them later on and build on them.
Obedience is crucial for a dog trained in protection, whether for sport or for real - even more if for real - and no matter how well behaved and obedient your dog is under normal circumstances, it is a whole different ball game in maintaining that level of control once your dog is working in full prey or defense drive. So that is one reason the training takes time, and it takes expertise - not too much obedience when young, then bringing in a TON of control and obedience when working in drive.
The importance of having this obedience base is the reason that Schutzhund clubs will absolutely want members to actively train in all three phases and not just in protection; they won't work a dog in protection if they are not satisfied that the owner has the skills and knowledge to put that base of high-level obedience on their dog and that the dog is under the owner's control.
Training a dog with questionable temperament in protection absolutely CAN make it more dangerous. Here is a dog that has no confidence, sees everything and everybody as a threat, would rather run than engage, but has over and over and over again been pressured to stay and fight. If the dog didn't have inappropriate fears before, it sure does now! Not fair to the dog, and a liability to the owner.