I don't know if I'm right. And I don't know if I'm advancing even a coherent idea about this.
I think in reality people do justify violence by the narratives they are exposed to. I think they see other people justifying hate and violence with these narratives, and they think to do it as well. I think narrative can give a concrete form to a pre-existing hate, frustration, anger or disatisfaction, and narrate a villain responsible for that feeling. These narratives inform and shape a person's worldview and their notions of who or what is responsible for how they feel and things they see happening. Narrative is an incredibly powerful way to guide people's actions.
Observe this: your narrative about the weakness of narrative in determining action, guides us to believe we ought not regulate narrative. You're shaping reality using the very tool you are saying cannot be used to shape it!
Double-think extraordinaire! No offence to you, just trying to (en)lighten this up.