The premise of this thread is that guns "work" or protect their user and loved ones. The premise is flawed and basically regurgitated propaganda from the gun lobby. Gun nuts repeat this again and again. So, OK, I admit that I'm enjoying pointing out how foolish this is, again and again. For the average gun owner, guns do not make you safer.
It took two stupid actions to have tragedy like this. First, the average Barney, gun owner, imagining he is some sort of ninja warrior and strapping the gun on. The second mistake was drawing that thing. Average gun owners that carry in public or keep the gun in their car have just made that first mistake. Too bad that you don't like it when I say it.
When going about in public, the only safe act for the average gun owner is to leave that thing at home in safe storage. If they don't then they are just a Barney and a hazard to those about them. As you infer, it is not strange that a Barney did something stupid.