Star Trek Fic Finder

I read a story -- I'm not sure if it was on AO3, the K/S Archive, or FanFiction -- where Mirror Spock journeys to the regular Enterprise. At the end of the story, regular Spock and Mirror Spock have an argument, where Mirror Spock is explaining why ruling through fear works better, and regular Spock is explaining why a civilized service where the crew has rights works better.  I remember that Mirror Spock made his argument first, and regular Kirk was afraid that regular Spock would find it hard to counter.  But regular Spock DOES counter it, and he manages to be himself while skewering Mirror Spock's arguments with devastating accuracy, making it clear that civilization is far superior to tyranny.  Kirk is sorry that he didn't have more faith in regular Spock's ability to stand up for himself and his ideals.

I'd especially love to read this defense of civilized behavior again in the wake of the American election, but I don't remember anything useful, like the title or the author or any characteristic lines.  Please tell me that it rings a bell for someone!

This is probably TOS, but I do occasionally read reboot.  I don't remember whether this was K/S or K-S friendship.

Thanks!

Edited to add:  I found it by pawing through my AO3 history; thanks to vicki_rae for mentioning this possibility!

The story is "Through the Looking Glass," by LadyRa.