I think most people will agree that avoidance is part of self-defense, but it is certainly not the be-all and end-all of self-defense.
Avoid the avoidable, and end the unavoidable as quickly as possible.
Some people go overboard with things. You say "Avoid the fight" and people will go to the extreme with that, they won't stand up for themselves when necessary because in their mind "avoiding the fight" means to not to engage in the conflict. A
In today's society a lot of people think "Either one extreme or the opposite extreme" things get narrowed down too quickly.
Not to pick on Wang, but in his original post.
"A: They are beating up your wife, are you going to do something?
B: She is not my wife. I don't know her.
B is safe, but his wife is not."
The assumption is that B. requires fighting in order to stop it. The truth is that there may be a possibility that B can be addressed without fighting. As long as the person doing the beating feels like his own safety is a risk. He will stop beating the woman and prioritize his own own safety. He may fight you, he may walk away, he may stalemate the situation. There are a lot of options. Calling the police is one of them. Or. Do both. Call the police, confront the guy. OR do all three. Call the police, confront the guy beating up the woman, and get into a fight lol.
For me personally. I've actually tried to help women in abusive relationships and all of them except for one turned on me. So I'm kind of on the approach with the mindset that I have more to worry about from the woman than the guy beating her. I'm more likely to physically assist if a woman is being attacked by a stranger. If a woman is being attacked by an abusive boyfriend, then I'm more likely to call the police and keep my distance. Not sure if you've ever experienced before, but there's nothing like trying to help someone from physical harm only to have that person turn on you and accuse you of being the bad guy. Abusive relationships have way too many layers for me.