Karkat has no problem killing other kids... but Sandy's a twelve and even though we haven't had them tagging, he feels sentimental about most of the twelves, so him murdering her would actually be kind of hard for him? Though he'd do it if he thought he was giving her a mercy kill. And considering what she's been through, I think that would count.

I think this is my round-about way of offering my loud asshole before he (maybe) goes off to meet his fate.