The problem that most seem to have is that the argument for criminal charges is illogical. Should every actor that handles a prop gun be required to be a gun expert? Has there always been an expectation that these actors be gun experts? And if the actors are required to be the gun experts, then what purpose does the armorer serve? In professional environments it is not normal to have to doublecheck someone else's work, especially when the person doing the doublechecking is not the expert.
But what about the point that Baldwin wasn't handed the gun, and told it was safe, by the armourer, but rather by someone who was not qualified to make that claim?
Seems to me it depends what the normal procedure is, and what the regulations say, but it's less that he should have checked it himself and more that he had no business pointing it and (possibly, allegedly - that point itself seems still uncertain) pulling the trigger, when he hadn't been handed it, and told it was 'cold', by that armourer.
Otherwise you would potentially have a position where anyone on the set could pass a prop gun around and wave it about and point it at people.