I've been trying to stay out of this thread but I have to respond to this. Your analysis of the Dawson College incident borders on the absurd. The police were on the scene within minutes. They responded by shooting and wounding the gunman, the gunman then committed suicide. Before the police could react, the gunman shot and wounded a number of students and killed one. Those are the known facts. Everything else is pure conjecture.
If a student or teacher or security guard (our wannabe cops are not armed, thank God) was packing a weapon, what would've happened? Well, as you say, in the best case scenario, he would have stopped the gunman. What else could have happened? Let's see, a) He/she could have triggered a gun battle resulting in a higher body count, b) He/she could have missed the gunman and shot or killed an innocent party, c) He/she would be dead since the gunman was better armed. Any number of these alternatives could have transpired just as easily as your "Die Hard" scenario. Life is not a movie.
I for one, am glad the only other armed persons on the scene were trained professionals - ie. law enforcement.