Step one is understanding you only control your own thoughts and actions. Step two is learning how to control your anger and use it as fuel for deliberate actions.
Honestly, I think Luigi here just followed this wisdom. Recognised that he was rightfully angry at the system and directed that anger at someone responsible. You only control your actions, and your action can be to shoot a motherfucker on the street ¯\_(ツ)_/¯
I'm not condoning or saying it's morally acceptable, but I don't think it's philosophically incoherent.
Ye, that's the point? The point is not to suppress emotions but to recognise them as they're happening to you. It's not even that there's objective value assigned to the emotions, it's simply so that you yourself can perform introspection of the kind "I did that action because I was furious. Now is that good or bad?". But it's still entirely okay to make a conscious decision of the form: