Alec Baldwin was given loaded weapon and told it was safe, court records show
theguardian.com
theguardian.com
Couldn't you ban this shit at the door and clean room it? Wouldn't this have been the initial reaction for prior incidents?
Even with defence in depth like you suggest where you properly isolate the guns and keep all live ammo away there still should be no excuse for not properly checking the condition of a weapon before using it.
In particular the handling rules are setup so if you accidentally break one or two no one should get hurt. In this case they were deliberately breaking several so only needed to neglect one and tragedy results.
The only guns I've ever held were shotguns for a couple of clay shooting sessions, and was told very firmly to never look into the barrel and to never point it at anything that it wouldn't be OK to accidentally shoot, even when cocked (don't think cocked is the right term here? In the non-straight form with an angle at the hinge exposing the middle of the gun)
But of course, "never point it at a person regardless of whether you believe it to be empty" doesn't work if an acting part requires you to... point it at a person.
Frankly (and not that I have any plans or dreams of being an actor), having read this story, if I were ever asked to point a gun at someone for a photo/video I'd just refuse unless I could first get actual firearms training to be safe, even if I were only due to hold a prop.