Okay, I'm pretty well in the middle ground as far as the sides of this debate.
In summary: treating the disease and treating the symptoms of it are not mutually exclusive. We can and should take care of both.
I think JohnSSC is unhappy about the increasing Us vs. Them mentality and in our country. This is paired with people being more isolated and not taking the opportunity to reach out and care about their community. This is very unhealthy and leads to a lot of animosity in our society.
I get the perception that a significant number of people who want citizens to arm themselves do so from an Us vs. Them mentality. If everyone is worried that "They" are going to attack "Us", that turns into a downward spiral.
The best thing we can do is make efforts to break down that divide.
However, E36 M3 Happens. No matter what you do, something is bound to go wrong. Sometimes that means having the ability to meet deadly force in kind.
Teachers who have been trained and certified would be excellent people to arm. They know their community and can read behaviors far better than an outsider. They aren't trying to judge the actions of a stranger in a dark doorway, they're reading the behaviors of children they deal with on a daily basis in a familiar environment. Teachers will have a good sense of what's going on.
Also, as I've tried to point out, the community will go nuts if a teacher ever presents a firearm in a classroom. Police have a mindset that they're behind enemy lines with a target on their chest and have a system that protects them if they react to a perceived potential threat. Teachers are in an environment where they care about their students. They do not view students as "them", the enemy. They will not be protected if they ever use a weapon, and will have to be absolutely certain of what they're doing before they fire.
Carrying a firearm does not make a teacher violent or cause them to inflict violence on their students. If a teacher carries and you ask them why, they'll probably say something like: "in case I ever need to protect my students from some threat." That's not violent. That's caring.
Not all teachers have to carry. Most won't. A few will. If those few hear shots fired in another room, you can bet they'll come running and that will prevent someone with nothing left to loose from going room to room and taking people with him.