Grant it, I don't know anymore of the situation, but do you CCW? I'm hearing reports from the Sheriff (as I type this) that he emptied out a full extended mag and was attempting to reload. I don't know about others (M2, Timbonez, etc can also comment), but I can draw fairly quickly and get a few rounds off...and I'm sure I can do that before a guy can empty a full 31 round magazine.
Now I'm not trying to say you're wrong (or right for that matter), and I definitely wasn't there, nor faced in that specific situation, but that's the whole reason people carry...to defend themselves and others around them. And I feel confident if I'm close to someone (7-10 yards) that I can draw, aim, and fire in less time than it takes a guy to get 31 rounds off.
But like you mentioned, thank God there were courageous people (I heard it was a female that got the gun) that had the guts to tackle this guy before he could reload and do it again.