Final answer:
A's inaction can be considered morally wrong as it goes against the principle of preventing harm to others. From an ethical perspective, preventing harm and promoting well-being are important. A's refusal to act disregards their duty to protect others.
Step-by-step explanation:
In this scenario, A's inaction can be considered morally wrong because it goes against the principle of preventing harm to others. While A may not have caused harm directly, they had the opportunity to prevent it but chose not to act. This can be seen as a failure to fulfill their moral responsibility to protect others from unjust actions.
From an ethical perspective, there are different theories that can justify the importance of helping others. Utilitarianism, for example, focuses on maximizing overall happiness or well-being. In this case, preventing B from doing something unjust to C would have a positive impact on C's well-being and contribute to the greater happiness of society.
Ultimately, it is morally wrong for A to refrain from preventing harm when they have the ability to do so with little effort, as it disregards their duty to protect others and uphold ethical principles.