Baldwin should have never pointed a gun at anyone and pulled the trigger. Plus, actors tend to trust those who hand them the weapon. I doubt many would know the difference in live, dummy, blank rounds. Not giving him an out, but film and TV armorers deal with this countless times with even more guns on set. Which also brings us to the policy of...
...NO live ammunition on set. How did that happen? Where was the armorer? Yes, I read some of the crew knew it was a real gun and decided to go plinking the day before with their own ammo.
Bottom line, the armorer screwed up by losing command of the props and a real gun. She should never fill those duties again, which is a shame since she is the Daughter of a renowned armorer.
Even uber leftist George Clooney said that it is the responsibility of the actor to verify that the weapon is safe. If it was some b-list actor he’d have been convicted by now