Speaking of perspective and nuance: violent self defense is justified to defend one's safety. But a slap by, let's be honest, a relatively physically weak person is not a credible threat to safety. It's just an insult.

On the other hand, physical abuse of women by men is much more common and dangerous, and there's a utilitarian argument that society should treat it more harshly. Not saying the guys beating up the other guy were moral, but it's easy to argue they were closer.