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Helping someone change their mind about something often comes down to presenting them with a choice: change your mind or bite a bullet. In other words, demonstrate that their position requires them to accept a conclusion they really don’t want to accept. This is why a good thought-experiment can be so effective.

People are loathe to change their minds, so the more difficult the bullet is to bite, the better. I like to say that I want someone to have to bite an explosive round, something they can’t just tolerate and act like they don’t mind it.

Earlier this year I wrote about how I respond when people attempt to defend the pro-choice position by appealing to utilitarianism. I start by responding with a straightforward thought-experiment:

Suppose a given person has a healthy heart, lung, kidneys, bone marrow, and blood. By kidnapping him, we could save five people or even more by distributing those body parts to other people that need them. Should we do it? Or what if it’s just one person that we can save, but it’s a more important person? Should we kill a homeless person if it means we can save, say, an important scientist?

This is a tough bullet to bite, but sadly, for some, it isn’t tough enough. Some people struggle to think clearly about murder. I suspect this is because when it comes to killing people, there are exceptions. You can kill in self-defense, most people believe you can kill in war, and while it’s more controversial, many believe you can kill in capital punishment. My colleague Rachel Crawford has also pointed out to me how deeply confused people are about revenge. Revenge stories are popular in books and film because we’re sympathetic to the avenger. It feels just for the wrongdoer to be punished in an act of vengeance. All of these problems make any thought-experiment about murder a little less effective.

But there are other actions that virtually everyone think have no exceptions, such as rape. Most people think rape is wrong, not just generally, but every single time. Utilitarians find it much harder to bite the bullet on rape. Here’s the thought-experiment I use after they bite the organ-theft bullet: