But those who seemingly express opinions that an armed civilian could have readily cut down or disabled the Aurora theater shooter are probably dreaming.
From what we've been told, the shooter was wearing body armor, and was armed with an AR-15 and other police-grade weapons. How effective would the average conceal carry pistol be against combat Kevlar?
Consider the North Hollywood shootout: Two guys in body armor with AKs were shooting LA cops and cutting their cars to pieces. Until better equipped reinforcements were improvised or mustered, the cops couldn't land an effective hit with their service weapons.
That's not to say an armed civilian might not get lucky in an exchange with a bad guy with superior firepower. Or at least buy some time to help others escape.
That's what happened in Palm Bay, Florida in 1987 when a gunman with a Mini-14 began random shooting outside a supermarket. Responding cops fell to his gunfire, but an armed civilian managed to engage the gunman for a time. The civilian didn't score any hits, and in the initial aftermath he was criticized by police for getting involved. But it was later acknowledged, his actions probably slowed the attack, and gave others opportunity to escape.
As for the Aurora situation, if concealed carry had been allowed in the theater, and someone there had a gun - he or she might have managed a lucky shot. Even if the shot didn't penetrate the attacker's body armor, it might have been enough to rattle his concentration and broken up the attack.
The again, any intervening civilian might have become the recipient of the bad guy's next lethal round, and it might have come before the first defensive shot could be fired.
Any kind of speculation is just that: Speculation. We don't know how it would have played because things didn't go down that way. Yes, conceal carry means if attacked, you have means at hand to defend yourself. But that's no guarantee you're going to prevail.
Fight the fight, and advocate for conceal carry all you want. Just don't get caught up in touting a fantasy that conceal carry makes everyone a superhero.