Not quite neutral
I know the piece wasn't intended to glorify them, but I still don't think it came off as neutral. The music (which I'd ordinarily enjoy) seemed overly reassuring and sympathetic while hateful and murderous plans were in the works. Maybe it's too heady a topic to take on in a single animation, but I think there was a lot of lost potential in depicting so many wasted lives (including the shooters) as a result of this environment. As it is, it sort of comes across like a love story (which I assume you didn't intend).