With this discussion, I got curious and looked into the definition of 'netorare' in a Japanese dictionary (Obunsha Japanese Dictionary 11th ed for reference). This is what I found:
他人の配偶者や愛人と肉体的な関係を結んで、自分のものにする。
"To form a physical relationship with someone else's spouse or beloved one and make them your own."
That's the core of the action, and everything else (e.g. a situation involving a mother, wife, sister, bully, ugly bastard, hot and rich, womanizer, childhood friend, crush, etc.) are just flavors authors use in their works.
If you take any situation in a piece of work related to this action, you will awaken different emotions depending on your pov as a reader and how the work itself is presented. If the pov is the one affected with this action (the most popular type of NTR in fiction works) then you're going to evoke a feeling of loss that could be severe, to the point that you could feel as if they died, depending on the connection you've formed with the person who was stolen (It greatly depends on how skillful the writer is and if that was their intention). If the pov is the one doing the action, then you will likely evoke feelings of power and pleasure from taking away someone else's beloved or the pleasure of exerting physical and emotional control over a female.