Not necessary, because “morality” is irrelevant. The argument concerns the relationship between legal penalties, guilt/shame, transgressions, and ignoring the welfare of others. We have no reason to think the author must have some belief about morality.

Necessary, because if this were not true — if NO actions that involve ignoring the welfare of others are transgressions — then the potential increase in transgressions from decreasing one’s guilt/shame would not be a reason to think there’s an increase in ignoring the welfare of others. More transgressions would have nothing to do with increasing instances of ignoring the welfare of others. So the author must assume (B) to preserve the link between more transgressions and more instances of ignoring the welfare of others.

Not necessary, because the concept of “people who are concerned about threats to their own well-being” has no connection to the reasoning. Although the argument does involve the “threat of harsh punishment for a transgression,” that doesn’t require the author to believe that people who are faced with harsh punishment begin to worry about their own well-being. A threat of harsh punishment can cause a chain of consequences without being related to one’s own concern for one’s own well-being.

Not necessary, because the carrying out of the threat of harsh punishment has no connection to the reasoning. The argument is based on the potential impact of the threat of harsh punishment. Whether this punishment is ever carried out doesn’t change anything about the consequences flowing from the threat of harsh punishment.

Not necessary, because the concept of “extremely severe transgressions” has no connection to the reasoning. The author’s reasoning does not depend on a belief concerning extremely severe transgressions. In fact, the author never comments anything related to different levels of severity for transgressions.