There are standards for lasers as they can produce significant eye damage. The ones we use on sights are tightly controlled. If you used a powerful one, beyond the standards, a reflection could easily blind a bystander.
Not a good idea and laser blinding weapons are banned. There are big flashing lasers to disorient folks but you couldn't carry them in real life.
As far as blinding the shooter - that's going to depend on distance. If you were farther back in the theatre - you will just be a target. I opine that the theatre distances were far enough that the standard handheld flashlight wouldn't be that terrible unless you were close.
My experience with flashlights in anything less than full dark adaptation and relatively close is that you are a target. Also, you have to aim it at the BG to get a direct beam, that might be hard in the uproar and again you are a target.
Close up and a surprise - worth a chance.