You missed the point in the illustration. From a social and legal context, once you have struck your adversary, you have crossed a line. Whether you are justified or not in crossing that line is a matter of much consideration of the context and situation.
For many practical application points of view, a punch to the face and a punch to the solar plexus are far different, but that's not the angle I'm looking at from. From the point of view of "do I go to jail for assault?" or "am I sued in civil court for medical damages?", it's a distinction without a difference
Then never study martial arts and just be a victim.