There's a lot to recommend giving a democracy-limited institution the legal monopoly on force. Some force is necessary, but really, very little. Particularly nowadays, where everyone is wealthy (on geological timescales, of course) and when people cause trouble there are a lot of sub-violent options.
But when we give that choice to someone, it doesn't make it easier. When we think about senseless violence like school shootings, we ask, what caused this? What caused previous US Presidents to bomb Kosovo or Yemen (the Yemeni atrocities are on-going)? I don't know, but our quick condemnation of violence should be the default in both cases.
Just because someone is allowed to choose violence doesn't mean that, when they do, it's justified, or even that they should get the benefit of the doubt. Imagine the reasoning the school shooter would need. It would be... insane. Impossibly high. And yet, "hey, they seemed like they were up to no good" is the standard used when we talk about war.
If you believe in God, know that he won't care about your flags. Hurting people needs to clear a high ethical bar, no matter what. That bar is so high that, for almost all sane people, it is prohibitively high. Sane people (usually) never, ever pass that threshold, and if it is passed in an emergency, they certainly don't go around hurting people, shooting or beating people over speculation or slight affronts.
Our military (and police) policy should reflect that. Humility, service, caution, and grace are the watchwords of all nuclear-equipped civilizations that wish to have a hospitable planet for generations to come.