From the last few paragraphs, it's not students who like firearms

that he needs to worry about the stability of.
It’s so complicated. On one side are all of my ideas about supporting students, honoring their individuality and their journeys, creating a safe space for them (and myself), not taking things out of context, not overinterpreting. On the other side are my memories of growing up in a situation where guns, people, and bullets had to be rigorously kept apart, lest they find each other in a tragic moment of instability.

She seems to be a good kid, Sarah. And I don’t know what she really thinks of gun advocacy and political failures that have cost us all these lives and our sense of safety as educators. I don’t know what she does on the weekends. I also don’t know if she understands emotions, or what real rage feels like. It seems to me no person who has truly experienced the full impact of their own emotions would ever go near a gun.
'Safe spaces' and projection of instability; see what I mean?

Certainly my predicament raises the whole issue of what letters of recommendation mean. But this whole thing just feels so, so … so much like creeping up the attic stairs, unzipping the padded case and running my fingers over the tendrilled grooves etched into the barrel of that old Browning shotgun. Peering down the chamber, I didn’t know how to say it then, but tools for killing will always be sacred.
I repeat: Professor, it's not your students who support the 2nd that you need to worry about the stability of.

You don't have the integrity to write a recommendation based on her known skills and abilities, and you don't have the balls to tell her "No, I won't, because you like guns and that scares me."  Wonderful.