I felt like I've left the key difference in the ethical stance between Spock and McCoy (Bones) unformulated.
Spock has made the phallic trito renunciation so that he feels like he is equal to others in the community. Thus, when he is calculating risks and outcomes and it is too dangerous for others to rescue or help him he will refuse/warn against help even though it means that he will lose his life. He wants the rest of the work-group to survive and carry on the work. He also will let himself die so that the prime directives of the work-group are obeyed.
With McCoy its a question of loyalty. When one of the main members of the work-group is in trouble then, despite the risks, McCoy advocates for loyalty and the potential sacrifice of the self for the other. Spock's "inhumanity" comes from his lack of loyalty and his failure to feel part of the "family".