I find these incidents disturbing simply because they happen but more so because of the way that folks seem to think they can be prevented... more rules.
All guns are always loaded. Period.
That really ought to be the only rule we need, right?
The "other 3" flow from common sense application of that rule. It turns out that "common sense" wasn't quite useful enough, so the "other 3" had to be codified.
Always keep the muzzle pointed in a safe direction. Why? Because all guns are always loaded.
Always keep your finger off the trigger unless you are aiming/pointed at a target that you are willing to destroy. Why? Because all guns are always loaded.
Always be sure of your target (really, that you are willing to destroy your target) and what is beyond your target (be sure that you are willing to destroy whatever is a reasonable distance/angle beyond your target). Why? Because all guns are always loaded. Not because you are intentionally shooting something but because you are intentionally PULLING THE TRIGGER. Doesn't matter WHY you're pulling the trigger. Demonstrations, unloading, dry-fire, you're intending to pull the trigger and the gun is loaded. Why? All guns are always loaded.
So, the obviousness of Rule #1 wasn't enough so we made 2, 3 and 4.
Those rules aren't enough, so we want to make more.
Why do we think THOSE rules are enough? You already can't possibly shoot someone without violating AT LEAST THREE rules. What good is the 5th, 6th, 7th?