I own (inherited) guns and live in a rural area, but taking a safety class made me realize I'm simply not the kind of person who will ever want to carry in public or preemptively escalate a situation with a firearm. So I think we're coming from a generally similar nuanced "centrist" background.
But what does "100% responsible for its use" even mean, modulo mens rea? If instead of an Uber courier, this had been someone knowingly working for a local gang who acted physically threatening, we would be viewing the shooting as a lot more justified, right?
I'd say that the shooter's perception was halfway to this, despite how we can Monday morning quarterback that the shooter should have perceived the human being they were aiming at was cowering and backing away. Human perception is terribly biased towards confirming what we think we should see.
Taking a step back, I'm not trying to excuse the shooter here, especially in any kind of fully-exonerating manner. But rather I'd like to avoid the situation being wrapped up and tied off in a neat little bag of "personal responsibility" where an 83 year-old gets "21 years" [0], and we ignore the more fundamental issues that created such a tragic situation in the first place.
Rather it's the surveillance industry's digital intermediation that makes it possible for the victim to be both perceived as an aggressive threat, while ultimately just being a regular peaceful person doing basic job after basic job (while shouldering an extreme amount of long-tail risk!)
(Also there should probably be some age limit at which there starts to be a recurring competence examination for firearms, like there should be for driving, or having signature authority on a bank account for that matter. But uh, good luck with that!)
[0] IRS life expectancy is 9 years, outside of prison.