The thing is that it still hasn't happened yet. Shooting a lock is idiotic. Picking it takes patience and that is something school shooters/bombers don't really have the time for. If the door is locked, the person is most likely to move on to find an unlocked room.
statistically it is impossible for it to not start happening eventually. at some point in the future a shooting will take place and the shooter wills start kicking in doors. eventually we will get to that 0.001 when it happens and we will not have prepared. its better to be prepared for something that may not happen than to not be prepared and the improbable become a reality.
1st a fire extinguisher would not incapacitate the shooter.2nd the teacher would not be able to stand up to a shooter. 3rd, a shooting wont happen when you are in class, it will happen between classes, where there are plenty of targets, and plenty of confusion to slip away with. while you are in class, there would be a probably drunk'drugged out parent coming to take their kid and leave for Montana, to get away from their spouse b/c reasons.
Have you ever gotten concentrated CO2 on your mucous membranes? Eyes, nose, back of the throat? It fucking burns. It's literally acid because it creates H2CO3 (carbonic acid) when mixed with water.
I'd rather rampage in a place easy to get into.
The data contradicts your "in theory" 's and your "theoretically" 's