Ask him why he let people die.

Specifically your comparison to Rachels dilemma about the bathtub death is inapplicable because in both cases the person had something to gain through the death of the child in the bath. You gave no reason why Kaine stood to gain from these deaths he let happen, which means in Kaine’s case there is a different base motive for acting against his values. I can hardly see how the bathtub scenario is applicable because of the difference in motivation.