I can't remember the name of the book now, but in high school we read a 'true' story of child abuse. I'm sure it was edited to both tone down and turn up certain elements, but it was pretty much a brutal shock to people who are mostly from decent families that love them. Whether the kids were rich, poor, or middle class in my school, just about everyone there could at least return home to parents that didn't commit those horrors.
I remember the diapers, the exposure to the elements, and the way the other children were pitted against the abused kid, and honestly? It was the emotional abuse that was the worst to read.
I'm disagreeing with your statement that "you're only allowed to use deadly force in proportional response," not with whether this case is being prosecuted rightly or not.
Mate, read that link I put in there. I can tell you, from experience, that if you shoot at someone stealing your property in Texas, where that penal code I posted is from, that exact portion of the statute is going to be used and you will not be convicted. It really is "anyone could have a gun or knife." At least Texas has it so just theft has to be during the nighttime, so I guess that's something.
You'll also get similar worded statutes in many other states in the US, several of which, stating this again, where I've had the misfortune of having to research those laws. And that "reasonable belief" part about exposing yourself to risk of serious bodily injury or death? I have seen it applied to people who are simply physically larger than you. Proportional response is a moot concept.