Supposedly the guy was on some sort of watch list, but I don’t know what that means (he was not on the main terror watch list, though). Even if they had put him on the terrorist no fly list and such, it wouldn’t have stopped him from buying guns legally and apparently he might have been an angry person but that isn’t a crime.
In terms of whether having armed people in the club would have helped, I think the problem is a lot of people have perceptions, based on tv and movies, about how easy it is to be the hero pulling a gun and shooting the bad guy.
Even on a shooting range, handguns are not that accurate, they love to show people shooting and hitting a target dead center, but handguns are not that accurate. I always shake my head when the cops kill some perp, and people are yelling “why didn’t you shoot the weapon out of their hand”, as if TV and movies were real.
Then, think about this one. When you are in the middle of something like that, it is akin to being in a combat situation. Soldiers and to a certain extent cops (SWAT teams especially), spend a lot of time trying to become inured to such situations, basic training and combat simulations are used to try and get them ready for what really happens…and even in that case it doesn’t help, and in a fitting parallel a lot of casualties, as many as 20% (least it was in WWII when my dad fought) were friendly fire.
Members of Navy seal team six spend a lot of time in simulations of for example hostage situations, under tense circumstances, and in a given year, at least at one point, that one team used more ammo then the entire marine corps in training
Now think about Joe/Jane Blow, who bought a gun pretty much by having a background check and signing his name and paying for it, maybe he went to a range once in a while to shoot. Person is out, is having a couple of drinks, is in the middle of a dark, noisy night club, and suddenly all hell breaks lose. The SWAT teams guys who went in there and got the bad guy knew they were going in there, and had training, but our friend? You see people dying, blood flying, people are screaming and yelling, and your adrenalin level goes through the roof, and at that point you are depending, not on cold logic and thinking, but on fear and adrenalin and whatnot. People in the military are trained that when this happens, that they can function, and they operate on instinct and training and muscle memory in how to act…but Joe/Jane Blow? They are going to be hopped up on adrenalin, heart pumping, scared, overwhelmed, and they are calmly going to pull out their weapon, discern friend from foe in the middle of a dark chaos, find the bad guy (who is spraying bullets all over the place, and those bullets travel, the muzzle velocity on an AR15 I hazard a guess is probably 2000 ft/sec at least), and take him out?
And if we have 50 people like that, freaked out, scared, perhaps a bit drunk, you think they are going to act like a cool, rational group of people hunting down the bad guy?
In both cases, what is more likely is the person either will never draw their weapon and try to flee, or will likely start shooting at shadows, and will end up hurting and killing innocents before they even got near the bad guy. Read up sometime on the simulations that cops use for hostage situations (and these days anti terrorist) and find out just how often they shoot the wrong person. In training for hostage situations and the like, Seals wash out (or they used to, according to Chuck Fararr) if they hit an innocent…and even with all their training, it happens.
The biggest problem with people carrying as a deterrent is that they haven’t been trained, and training is not just about how many times you hit a bullseye on a range, ti is about being able to function with the noise and chaos that surrounds situations like this. Another factor is that people without that kind of training tend to hesitate, because they are likely decent people and have the instinct that is another person they are shooting it, the military and such spend a lot of times figuratively beating that out of recruits, to forget the other person is human that they are attempting to take out.