Interesting discussion. I'm not sure what "protection" always means. What does it mean to the handler? What does it mean to the dog?
When I was a kid we had a GSD, Brenda. Brenda was a nice dog. Everyone always commented on how gentle she was. She had issues with the mailman, but that was pretty much it. She wasn't one to alarm bark when someone came to the door. Here ears would go up and maybe she'd growl softly, but that was about it.
My dad had ALS. He had been in the road construction business and, being Italian (his parents came off the boat), had worked for several companies owned by Italians. Who all spoke Italian. The people he worked for and with were very tight with each other, and would come to visit him after he got sick.
I remember this one guy who came to visit dad every week. He'd come into the house and Brenda would pretty much ignore him while he and dad visited. Now I have to digress just a bit. Dad's family spoke Italian at home and he didn't learn English until he went to school. This wasn't uncommon for the children of immigrants in the 1920s. So dad and his friend Tony would break into Italian, usually when we kids were around, for reasons they never explained to us
One day dad was standing in the living room, on crutches, talking to Tony. They were speaking Italian, the conversation was quite animated, and Tony was waving his hands around. No, it isn't a stereotype, Italians speak with their hands. Anyway, as I said, the conversation was animated and loud and Tony was waving his hands around and Brenda just went nuts. She got between dad and Tony and barked and growled at him and pretty much scared the crap out of him.
Was she trying to protect dad? I think she was. Would she have pressed it if Tony had taken an aggressive action towards her? I have no idea. She had no protection training at all, so I doubt it. On the other hand if you had asked any of us before this incident if Brenda would react the way she did, we would have all said "no".
Now it is 45 years later and we have Hans. Hans comes from working lines that are titled up one way and down the other. He has much more drive than Brenda ever did and alarm barks his head off when anyone comes up to the house. Or walks by it. Or ... you get the picture. We play tug games with him, but he has had no protection training. He is a naturally confident dog but we have done nothing to increase his confidence under pressure.
I have no reason to believe that he would attempt to protect his humans in a crisis. Still, watching him and how he behaves, I think it would be a bad idea for anyone to get into my wife's face and start aggressively yelling at her when he is around.