Willie, he's tying into one of my previous posts about individual responsibility as opposed to the individual being protected from all harm by the nanny state, and the latter resulting in excessive regulation and litigation. So, I'm responding to his criticism of my inclusion of the McDonald's coffee case.
Personally, I think it's on point. Many things out there can hurt us if we are careless. Often as not, though, when we get hurt it's our own fault. The lawyer who came up with the concept of "attractive hazards" should have been tarred and feathered, but I suspect he occurred a few generations too late for that result...
How it all ties into the OP is that the fact of the unlocked gun is something the gun owner may regret, and something that most of us might recommend against; but the shooting is the responsibility of the shooter. A 14yo is old enough to know better, unless she's mentally incompetent.