Dbfan and critic said:
I would like to say there is no evidence suggesting KR can only affect evil people/people who have killed
Heck sans Threatens frisk even if they haven't killed anybody
Sans threatens Frisk because Sans is the vastly superior fighter, and in a non-genocide timeline, even the strongest Frisk gets during the regular (i.e. no OF or Asriel included) game isn't that high (at least not compared to Chara in the genocide route). I doubt KR affects everything equally, especially since the text in the battle explicitly implies the weight of your sins is literally what's killing you.
"*KARMA coursing through your veins."
"*Doomed to death by KARMA!"