evolved to be more sensitive to light, resulting in everyone tending more towards malevolence, and barbarism, and queer coded villainy.
You know, I spent the whole episode sort of wondering if they were going to try and speculate that all the species of the Mirror Universe are campy jerks because in that universe the Progenitors were campy jerks. But I suppose I'm glad they didn't try and explain it, and it's still just a little pastureland for the actors to go chew scenery.