I can only fault Alec Baldwin for running a production that already had a perceived gun safety issue and not sorting that out before proceeding. I can not fault him as an actor, doing his job and carrying forward with the scene as directed. Tom, you keep using the word "decision". I don't see it as a decision but part of the normal course of duty as the actor in the scene. The real problem is that a REAL round of ammunition found its way into a movie set gun. That is a possible criminal act and should be the focus of the ire instead of blaming the actor like they are the only one responsible. Just my opinion and does not diminish the horrible tragedy for all affected.
Maybe a new approach needs to be had on set? Maybe new special "set guns" need to be made which do not have barrels but are like cap guns but also create a muzzle flash artificially. Then audio can be added in post. I see no need for real guns to be anywhere near a film production.
The "decision" was the one to not confirm the call of "cold gun" from the AD with a simple backup check of the unholstered pistol for possible loaded cartridges. How much of a hurry could the production have been in that they could not afford the miniscule amount of time to make a life saving final check for loaded rounds?