How many school shootups have been "in the heat of the moment"? Every time the police follow up, it looks pretty apparent they were planned. I mean, who has full body armor available "in the heat of the moment"?
(Aurora and the most recent shooter were both in full body armor)
Even when these events are planned, there is still a time when you go "I need a big gun" to getting one. If mom has one in the closet, this obviously makes that event happen instantly. If there are more roadblocks to the process of acquiring an assault rifle, wouldn't it be worth it even if it saved a single life?
(Aurora and the most recent shooter were both in full body armor)