He was well enough lit that people could describe what he looked like and what he was wearing. From what I have heard he was standing directly in front of the screen so he would have been lit by the projector. Also the muzzle blast from his guns would have made it pretty easy to know where to shoot. I have been in room full of tear gas on multiple occasions and yes it does burn your eyes but it doesn't keep you from being able to see. Since he was standing right next to smoke it have been more of a problem for him than me because the mask doesn't make it easy to see through smoke. It would have spread fairly slowly so unless I were near it I would have time to gets off some shots before the gas got too bad and if I was that close I wouldn't need to see that well to hit him. If you had been trained with tear gas like most members of military have you might even have enough common sense to hold your breath or at least breathe through your shirt. The gas would be a complication but not an insurmountable problem.

As for the vest while I am probably above average in my marksmanship skills my skills are not extraordinary or all that uncommon and would I like my odds of getting in an incapacitating shot with one of the 15 rounds in my 9mm. Even if all 15 rounds went into the vest, which they wouldn't, the distractions might have been enough to let more people get through the door. Since I wouldn't have fired all 15 at once 3 rounds to the chest would have stumbled him if he got back up I would try for head shots or maybe even just shoot his legs. I doubt he would have ignored having his knee cap blown off. Hell since he didn’t appear to want to die for all we know he would have fled as soon as he realized someone was shooting back, he sure didn’t try fighting the cops. I bet I would be a better shot with my 9mm standing in the seats than he would be with that 100 round drum and a gasmask. Ever fired with a gasmask on? Odds are he hadn’t either. I have been trained to fire wearing one and I still can't shit with one on. So while I can't garuntee I could have stopped if had been there armed the idea that I wouldn't have stood a chance is misguided at best and either way I will take the 9mm over throwing my popcorn at him and trying to decide if laying on the floor and praying gives me better odds than trying fight the mob trying to get out the door.

I have seen several people making the same half assed arguments you are making and they all come down to nothing more than people who have no idea what they are talking making shit up because they the answer they get when they jus tmake shit up and in most cases they don’t really care because they are just trying to leverage this tragedy into promoting a political agenda. The real problem with guns isn’t crazy people who shoot up theaters it is thugs and sociopaths who shoot up neighborhoods and morons who don’t have enough common sense to properly secure their weapons.