Granted, Alec Baldwin is a complete shitbox. Can't stand him. But, on a movie set, you should have zero worries you are firing a real gun. Why were they using a real weapon, and more importantly, why in the hell would live ammo be on the set?
If you're a complete "guns are bad" dipshit, I would not expect you to know anything about guns. If it comes out he was firing the weapon at cans with the rest of the jackwagons, then he might be guilty of something. If he was just a dumbass playing with a "toy," I guess I can't blame him.