As a version of the "trolley problem" it seems completely unrealistic, but here's a plausible real-life scenario where someone could stop an atrocity by uttering a racial slur: You are an undercover government agent, who has been tasked with infiltrating a far-right extremist group, in order to determine whether they are planning any violent attacks, and to gather evidence to enable their arrest and prosecution. In order to be accepted as a member of the group, you must utter racial slurs. If you refuse to utter them, the group will not accept you as a member, you will fail to infiltrate them, their planned terrorist attack will not be discovered in time, and innocent people will be murdered in an attack on the minorities the slurs target.