You have quite different intentions when you're punishing your child because he didn't do his homework vs. when you're punishing your friend because he stole yo

You have quite different intentions when you're punishing your child because he didn't do his homework vs. when you're punishing your friend because he stole your girlfriend. In one case you aim for blood, in the other - for betterment and growth. Intention makes all the difference here, otherwise, they are, like you say, both just forms of violence.