Well you are entitled to your opinion. I certainly don't understand the notion that quickly changing a magazine is some sort of accomplishment.
The only possible time this could be an impediment would be when there is someone within arms length who was still able and had the nerve to try to physically stop the shooter while reloading.
You are not going to even be able to cross 5 feet before even a novice will have the weapon loaded and you will die.
When shots are fired, people run. Fewer people would have died if the whole theater charged him right after he started shooting, but that's not realistic, some of the chargers would have been the "fewer people" and instinct is to try to escape.
The former situation is what happened in Tucson. The shooter went to change magazines and a woman intervened, but he was standing in the midst of people, not a short distance away aiming up into theater seats. According to reports I read, she grabbed the magazine while it was in his hand. It's quite possible the only reason she was able to was because it was long enough for her to get a hold of it.
Apparently after losing that magazine, no one was able to stop him from loading another standard length magazine, but luckily it malfunctioned.
I don't know and you don't know if not having a 30 round magazine would have lessened the carnage in this incident.
In the Aurora shooting, it appears that he chose the time to stop shooting, no one was able to attempt to stop him when his AR-15 finally jammed and he changed to another gun.
Therefore it seems to me likely that no one would have been able or willing to try to stop him while reloading and having to change magazines would have likely had no effect on how many people he was able to shoot.
I wasn't there, neither were you. No one really knows.
I need more than conjecture to start down the slippery slope of banning any firearms or accessories because it's possible it "might" do something.