If the little girl had smacked the little boy, she would have been punished. Also, you're advocating the lesson that boys should be afraid of reprisal, not that boys should be respectful of other people's stuff, which is the wrong lesson entirely.

You're right, why aren't more people advocating we teach our kids to use violence to solve their problems?

So knocking down castles is okay if you can also overpower the builder so she can't hit you?

Is it okay? Most would say "no", especially when applied to the metaphor that the blog writer is going for. Is it how the larger world works in many cases? Sadly, yes.