Because they can all do it. Freaky things happen with guns that is why we should respect them and be aware that they are dangerous.
Standard drill at Gunsite used to be (and I think Ken Campbell still does it) is to fire a Smith & Wesson auto pistol with the magazine out. Overengineering cannot overcome accidental discharges, especially when there is stupidity involved.
I am all for not coonfingering, but riddle me this, is there ANY chance a striker or hammered firearm goes off without being touched, moved, jostled, or dropped? Like in a case, safe, or otherwise untouched, left alone?
I doubt it, and if it could, no one would use a safe for easy access in their house, because it could potentially just go off while you are at work, or shoot you in the foot while you walk around your room. I think this is what the INGOers are saying.
I'm not talking about loading or unloading. The machine is safe, it is always improper handling, which includes not loading/unloading in a safe manner, dropping your firearm, or leaving it in a loose garment to move around as it pleases. The mechanics are safe. The user is not.