During my military service, folks newly assigned to the command were all required to recertify on small arms safety protocol, no matter their rank or experience. (Our CO was unwavering in enforcement of this requirement.) For awhile I acted as the range safety supervisor, as backup to the instructor who had primary responsibility for instruction, grading, and certification of the new crew members: my role being mostly to ensure that a second set of eyes was focused on safety when the range master was otherwise occupied. We kept detailed safety records for our performance reviews.
Can you guess the number one safety violation? Negligent discharge. Even among otherwise experienced personnel.
As much as I've enjoyed Mr. Baldwin's acting performances over the years, my awareness of the lethality of even the smallest of mouse guns predisposes me, in this case at least, to assume he is guilty until proven innocent. Sorry Alec, but you can't un-ring this particular bell: ignorance and inexperience are no excuse. That noted, I also suspect that an equal share of culpability lies with the armorer who left a loaded weapon in the hands of the firearm equivalent of a muggle. A reasonable person - especially one charged with the duty to supervise the safe handling of loaded weapons - should know that such actions amount to wanton disregard for life and safety, and at the very least constitutes gross negligence, and conscious indifference to the harm that in this case did indeed occur.
We can debate which of these two is the more culpable, but I'm pretty sure most of us would agree that they are both at fault, and both should share the blame.