If NK looks scummy, great, we kill them. But we don’t hunt the NK over killing other players that we suspect are groupscum. We have other scumreads, we don’t immediately need to go NK hunting.
The idea seemed less to me as “leave NK up to kill groupscum” and more “we don’t need to focus down NK because they have the potential to kill groupscum and they’re less of an inherent threat than groupscum”.