I don't understand how "more guns, not less" is supposed to be the answer. Let's look at a scenario in the current world and in the "more guns, not less" world.
Current world: A guy walks into a school and starts shooting students and teachers. Many people die until eventually the shooter kills himself.
"More guns, not less" world: A guy walks into a school and starts shooting students and teachers. In theory some teacher bravely starts shooting back at some point and possibly kills the shooter. Likely between when the shooter starts and when he is killed, some number of students/teachers are killed.
In both those scenarios some number of students/teachers are killed and the shooter dies. The only difference is how many students/teachers are killed.
How helpful is the consolation to the parents/siblings/loved ones of the dead in the latter scenario that "at least fewer people died than if that teacher didn't have that gun?"
Their loved ones are still dead! All the people in the room still witnessed a horrific thing and will need trauma therapy for years!
Why don't we just work towards the world where there are no guns? If the guns were not available, then none of the above scenarios could happen and no one would have to die or be traumatized for life.