In the US, “I didn’t know it was loaded” is not a legal excuse. Try it in court yourself and see how far it gets you.
The VERY first rule about firearms is that 'All guns are treated as if loaded at all times". And you NEVER trust anyone when they tell you it’s unloaded. You check yourself to be sure. This includes a prop gun handed to you by a prop person who announces “cold gun!” It takes mere seconds to check it yourself. No excuses…
Your last paragraph shows even more negligence on the part of Baldwin. He broke another cardinal rule of gun safety by pointing an assumed unloaded gun at something he wasn’t intending to destroy or kill. And coupled with supposed rush to film, added to the complete breakdown of basic common sense firearms safety rules.
There was negligence all around that ended at Baldwin. And no one else gets away with that much negligence, (remember he was also a producer - The Boss), in a fatal “accident” and doesn’t get tried in court. Because Baldwin is famous and rich should not prevent his day in court.