The angle I’m looking at is that group psychology is very different from individual psychology. Mobs have a mind of their own and behave completely differently from any individuals within that mob. That leads to a few other related thoughts.
Hypothetical;
Someone fires a shot. You reach for your gun and scan for where the perp is. By the time you clear leather and scan more than a few degrees of arc, you see hundreds of people with guns. Oh, and a few hundred see you with a gun too.
What happens next?
Well, if someone gets a shot at the perp, that person may be confused for the perp by those that didn’t hear the others say, “There he is! Get him!”. And if someone gets a “false positive” and takes a shot against someone they think is the perp, then it gets even more interesting.
And that’s just the first 2–3 seconds; no telling where it goes from there. If even 1% of a group of 50,000 gun-carriers is less than 100% accurate in both target identification and trigger discipline, that’s still 500 people that could cause some serious accidental damage. All it takes is one screwup.
On the other hand, if the only ones doing the shooting are people with badges, people with snazzy black suits complete with earpieces and cool shades who have many hours of training for engaging in areas with a lot of civilians around, and the perp, the equation is a lot simpler all around and the body count a lot lower.
In any event, this isn’t like going into the 7/11 where it’s just a few shoppers, a cashier and a crackhead. The tactical situation is much different, and I don’t think any civilian has the ability to handle something that even trained professionals have difficulty with. When a tweaker points a gun at a guy behind a register, there is no question who the samaritans should point their guns at. There is far lower risk of collateral damage. Put in enough people to make LOS hard and positive target identification harder…. well, that changes things. A lot.
Like I said a few times, that may not happen but there is a non-zero possibility of it, and that is enough for anyone concerned with public safety to balk.
Hell, I’m wondering where you’d get 49,000 level-headed folks in the first place!