Absolutly, much like saying if you had a wench you could fix your car... Well you have to know how to use it, and you have to know when not to use it... And lots of times a fool with a wrench has made things worse.
There wasn't much that would have made that situation worse ... Its nice to speak in a condescending tone about how "doing something" might have made the situation worse, but I disagree and think it was already as bad as it could possibly get.
That means a CCW holder could have been justified in taking a shot even in a dynamic environment where he has potential to hurt/kill another innocent. Police engage criminals in situations all the time that aren't cut and dry, because they believe that if they DO NOT engage, that more harm will be done than if they DO ATTEMPT to engage.
If someone in the first or second row had a good light and knife on him, it was possible he could have flashed the guy and lunged at his throat. Yes its conjecture.
Just as likely, is someone near the back who could see what was unfolding and had a firearm on him, could have fired a few "risky" shots at the guy and taken him out after only two or three deaths.
I think doing nothing--because it might be risky--is the bureaucratic solution and not the one that made any of our countries great or inspired any pride.