I believe many people who are going through-or have ended- a SM can strongly relate to this.
Wow!! As someone who suffered this kind of abuse for 14 years, this is spot on. These types of people are dangerous as they can make the most stable soul crack and crumble...and they do it with a smile on their face. Pure evil.
As well, if there are children in the picture, their is a strong or some say certain chance that the narcissism will be passed to them, and the cycle perpetuates itself. (Not my opinion, but consensus from many in the professional psychological community).
These people don't choose this for themselves - it's an unconscious choice; really their self-esteem is in the toilet due to the abuse they suffered at the hands of their parent(s) and their narcissism grows to cover it up - but knowing that does little to nothing to mitigate the damage they do to everyone around them. Kind of like a zombie bite (that one is my own opinion).
My own abusers, one passed on and the other estranged permanently, will never have my forgiveness, because there was never any effort to change: no apology, no acknowledgement of their tyranny, no effort to make amends, and blaming the victim, among other things.
On the other hand, they don't have my hate anymore either. That's too much energy for me to give away. I pity them, but I would never comfort them, unless and until they seek professional help - but IMO I don't see that ever happening.
The only thing that saved my own ass, was my grandmother - with her kindness and compassion, and providing me some escape from the madness that I lived through from age 8 to 18. That sliver of sanity is very strong now, but on a daily basis I need to constantly monitor myself, lest the monster pries the door open.