Tabula Rasa: Good vs Evil

Ostensibly Tabula Rasa is about Kate and her "clean slate" on the island. but it seems to me to follow directly from Locke's "light and dark" discussion on the beach in the pilot. Several characters are presented in this episode as having indeterminate morality, most notably Kate. It is revealed that, before the crash, she was a prisoner of "the law" for having committed an unknown crime. And yet she shows real compassion for the people around her, including the marshall himself. She helped him on the plane, and she had a chance to kill him on the beach, but didn't. It isn't clear from this episode whether the marshall himself is good or evil. Jin and Sawyer both seem to be less than stellar individuals, but both show flashes of compassion in the episode. Perhaps most enigmatic is good old Locke, already a figure of mystery. He seems to be a decent chap in his relationship with Walt and Michael, but oh, that episode-ending, bone-chilling scowl....