Teachers, for the most part, are snowflakes. You can’t “force” them to carry a gun, and you certainly can’t trust them to use it properly.
Teachers are the folks saying Columbus committed genocide. Actually, this may point to deeper societal problems that cause young men to be full of hatred and self-loathing.
The point is that the weirdos do not know who the snowflakes are and the prospect of walking into a school with a gun and meeting someone with a gun also is a deterrent.