[nomadking]

The Bataclan hall attack was brought to an end by armed police officers. If somebody in the hall had had a gun and used it, the attack would have been stopped earlier. On the other hand, how likely would it be for somebody to take a gun to a concert? As for the suicide vests, that shows that banning guns isn't a solution.

A mass gun attack only works if carried out from far enough away to avoid return fire or where it is very unlikely that anybody else is armed. Nothing much can be done about the first, only about the second.