Ok, let's do this. Buckle up kids. It's time to drop some hard truth on the myth of the good guy with a gun. Even better, we're going to cross post it so everyone can see it.
First of all, teachers don't have proper supplies because y'all don't want to pay for it. You expect me to believe you'll buck up to buy teachers a handgun? So hire veterans to guard the school? With the same money you won't contribute for standard school supplies? Ok.
Second, and here's where you need to pay close attention. A 'good guy with a gun' is only making a bad situation worse. Let me tell you why. We'll use the Florida event as our model.
We have a single bad actor with a high power, high capacity weapon intent on causing a mass casualty event. We have one or more guards with handguns patrolling the grounds. The rifle has range and capacity, and the actor has surprise and timing on his side. The guard is eliminated from the equation and the killing continues with barely a pause.
Give a guard a rifle to better combat our bad actor? Is he carrying it at all times or is he required to store it in a secure location? If he's carrying it at all times, the bad actor can walk through the metal detectors with no issue, take out the guard who isn't expecting it and begin the rampage with a weapon you provided.
If the guard has to keep the rifle in a secure location, it's an extra 5-7 minutes of response time. 20 more casualties while he's running for his gun. That clearly isn't an option either.
Instead of removing a destructive element from the equation you've added another one. Now you have a bad actor exchanging fire with a guard. High speed destruction heading in both directions. Good luck to anyone in the crossfire as they're as likely to get hit by the guard as they are the bad actor.
A clearly armed guard at the door will deter violence? Again, the actor has range, speed, capacity, and surprise. The guard will be the first person removed from the equation, and you left him exposed out of cover.
You ask what happens when that the guard is inside the door with a weapon? Well, he might have a chance but I'll point you back to the previous paragraph. An actor intent on mass casualties will start during a high traffic period. The guard will be returning fire and adding to the damage.
What about a plain clothes guard or an armed teacher? That's nice until the first response team arrives and can't immediately identify the bad actor for neutralization. Body count continues to rise in the confusion, introducing the possibility of adding our savior to the list.
This is just the beginning of the equation for a single bad actor intent on causing a mass casualty event. There is no positive solution involving the addition of more weaponry to the equation.
Now ask me about what happens when there are multiple bad actors in play.