Let's play a scenario.
Let's say there are 2 children and one is older and a whole lot stronger. If that stronger child, let's call him Greg, pummeled the other child's face and broke some of their bones but then excused his behavior by saying, "well, Bobby hit me first, plus, I could have killed him if I had wanted to. I'm so much stronger and more powerful than him."
Are you going to praise Greg for showing restraint? Or are you going to scold Greg for pummeling Bobby's face and breaking some of his bones?
If Bobby actually hit him first I am not going to say shit, because Bobby asked to have his ass beat.