Why does it matter if it personally occurred to him or someone related to him? It happens to plenty of people. You can have empathy for people not bound by blood.

Of course you can. But where does it stop?

There is a great deal of injustice in the world. Psychologically healthy adults have learned to add a reflection step between anger and action.

By all evidence, Luigi is a smart guy. So one can only speculate on his psychological health, or whether he believed that there was an effective response to the problem which included murdering an abstract impersonal enemy.

I'm stumped, honestly. The simplest explanations are mental illness, or a hero complex (but I repeat myself). Maybe we'll learn someday.