It might have worked, but unless you aimed it perfectly the first time, it also would've given the shooter something to aim at in the middle of an otherwise dark theater. I suppose if someone wanted to volunteer as a sacrificial target, a laser would've been a good tool for the job.
Even if it did blind the shooter, there's no guarantee they would've stopped shooting. It's not like the shooter was being very careful about his choice of targets.
As for shooting the guy with a normal gun, you don't need to get a head shot or chest shot on a civilian target to disable them. He had almost certainly never been shot before, and the shock and force of impact -- even with body armor -- would've stunned him for several seconds. That would allow time for a follow-up shot, or for a good old-fashioned tackle.