I'm not exactly up to speed with American regulations, especially because they vary a lot depending on the location, so care to elaborate on that? As a European with the equivalent of a CCW (among the other pile of licenses I could plaster my walls with, because I'm also a collector and a "traditional" sporting as well as practical/defensive shooter in IPSC and similar more local entities) I'm curious as to what's considered over-regulated.
Worth noting that some guns don't have a manual safety. GLOCKs are a notable example - they're extremely common among American LE and "don't have a safety" (or rather, they do, but it's not a switch you flip, it's built-in the trigger, pulling it gradually releases the safeties). Which makes them a bad idea for people with poor trigger discipline as opposed to guns with a safety that can render the trigger useless. GLOCKs also happen to be prevalent in the FBI, they have some SIGs but mostly GLOCKs, and GLOCKs also happen to be their off-duty weapons of choice, so I'm willing to bet it was a GLOCK.
Regardless, the gun was fired because that idiot picked it up incorrectly, i.e. with his finger on the trigger, which should be considered the only safety for discipline purposes independently of whether of not a gun has a manual safety as well.
That being said, carrying a gun with a chambered round and the safety off can be perfectly fine (revolvers typically don't have safeties and because of their nature they always have a "chambered" round), the point is that they must be handled religiously. Failing that, holster or not (quality modern guns are able to be carried safely even without a holster even though it's not ideal, aside from those guns that are downright designed for holster-free carry), safety or not, chambered round or not, bad things will happen.
If my memory isn't failing me, the underlined part is dubious at best. In an "I'm not racist, I have lots of gay friends" kind of way. And I'm no "shall not be infringed" fanatic, not only because I'm not American, but because I believe gun control is a good idea - but not gun suppression, every law-abiding citizen with the physical, psychological and technical requisites should be able to own guns. That way, gun-related crime is very rare, mass-shootings are unheard of, and gun owners don't have to worry about gun-grabbing politicians or stupid limitations such as the 10 round magazines for "assault rifles", whatever the hell they mean by that other than "scary-looking semi-auto long guns".
I hope there's irony there, otherwise this is a prime example of hoplophobia born out of ignorance and/or ideological indoctrination.
The underlined part needs a lot of elaboration on your part. People use guns for hunting, sports, collecting purposes, even just fun (what's wrong with plinking if it's done safely and responsibly, pray tell?) and defense. The latter is needed by everyone. Do you live in a country where the police can predict crimes and take preemptive action, teleport instantly to stop a crime or some such? No? Then your claim is null and void. It'd be null and void even if we weren't talking about defense, because there's absolutely no logical reason to prevent law-abiding, able-bodied, sound-minded individuals to engage in a range of activities just because they involve those scary, evil guns. Shall we ban, say, car racing and skiing as well while we're at it? Accidents in car racing and skiing are enormously more common than in shooting sports after all. And you don't even need a license to ski! Someone I know who was hit by a criminally idiotic skier cutting a blind turn at 70/80 km/h would have something to say about that.
Except that's wrong and laughably simplistic, as even a simple, far-from-complete wikipedia page shows. Not to mention, the CH/IT/CZ are doing well when it comes to crime (and other issues) compared to European countries with stricter laws. Besides, the fact that a constitution or a code of laws regulates the matter is utterly irrelevant, Mexico is a good example of that since you mentioned it. It's almost as if things changed over time.