BIll,
Perfect. Give me an example of a police station that was targeted in a mass shooting.

Here was one just for you:

http://www.fox5dc.com/news/local-news/dc-native-leaves-job-as-teacher-to-become-police-officer

Teachers can and do become cops, Bill.

More important to the discussion than what set of skills are interchangable, is where an individual falls on the "wolves, sheep, or sheepdogs" profile. Kids can be wolves, as can, unfortunately, teachers, or cops. But, everyone falls somewhere in that set, including the cop who was suspended and later resigned at Parkland. He was a sheep.
I will never believe that all people employed in a profession fall into a single group. There are teachers who would make very capable sheepdogs, Bill. Not likely you, since you have already made the argument that it isn't possible for a teacher, but, I have known a few that I would trust my life with.
I care not in the least about "treatment" of an individual who can or would take arms up against innocents. Much like the Israelis, I want the potential target hardened, and clear thinking about protection and survival of the potential victims to be the main consideration. The bad guy can go to hell, or, to go meet his virgins. I don't care if he is 14, or 40. Nobody can save you when you are at the point of shooting up a school.
Nipping a problem in the bud only works when it is a bud, not a full bloom problem.
The bad actors on the left made a point of making sure schools were very clearly unarmed and helpless until help arrived, and that that fact was broadcast and recognized.

None of this was unpredictable.

Ted