A hypothetical question of ethics comes up resulting in two or more of your characters debating the “right” answer.

The what now?

There is a runaway trolly and if you do nothing, it will run over five people. However, to save them, you will kill an innocent bystander.

The trolley problem is a series of thought experiments in ethics and psychology, involving stylized ethical dilemmas of whether to sacrifice one person to save a larger number.

Trolley problem, From Wikipedia, the free encyclopedia