A true 'protection' dog is one that is well socialized and comfortable in any and all situations. That way they are calm and thinking and able to make the right decision as far as recognizing a true threat (mass murderer) from a 'fake' threat (child's friend play wrestling with dogs family member) and make the correct decision to step in or not.
So I know my 'job' with a puppy until they are done maturing mentally and physically (18 months to 2 years) is to give them the confident and secure socialization and upbringing so they will be that thoughtful and thinking dog. So I take my pups EVERYWHERE and have them meet EVERYONE so they learn that the vast majority of the world is a good an happy place they can feel confident that I am guiding them thru. My pups learn to look to me, learn from me, and cue on my behaviors for what is normal or NOT. And if I say it's ok, then it is, even if it's new to my pup.
So later on when that mass murderer is coming at me, my adult dog will IMMEDIATELY notice the difference in both my behavior and actions as well as the mass murderer.
Friendly happy puppies willing to greet the world is what we want. Their natural aloofness usually starts kicking in around a year for my dogs, so they no longer LOVE everyone, just their people and others are ok.
Dog classes are the best prep for alot of the socialization that I may find hard to plan and do on my own. Between puppy kiindergarden followed by as many obedience classes as I have time for an can afford, I end up with a great dog.