It's not about listening, it's about the commander issuing an order, which has the same weight as a judge issuing a warrant, to actually take the weapons from his possession/home. An order that MPs and local law enforcement can legally go and execute.

Though I think this whacko is ultimately responsible for this ill and evil shit, I think the commander might've been negligent here not doing more. (If indeed the gunmen was institutionalized, and the commander was aware of that fact.)

And yes, I think the lack of any red flag laws in that state is insane, and that such laws likely could've helped here. I'm just making a point that more realistically could've have been done given the situation as it existed in that moment.