We rarely grow when we're happy, we grow when we hurt.
What could be more unjust than hurting an animal or a child? When you've been gifted dominion over something, that responsibility is real.
I don't know how people box for a living. I don't know how they can just hurt people for a living and be OK with it.
When I was young, I remember having a particular pain about injustice. Suffering hurt me.